<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019cdd48-28f7-780b-8cfe-a74018fb3e7c,g:cd15c398-d7fd-4f1a-9aef-8b5b3239ec24-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="simple" xlink:href="pstl-20260331.xsd#ConsolidatedBalanceSheetsUnaudited"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019cdd48-2a4f-7dd8-a1c8-68025883dbce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019cdd48-2a4f-758b-8c42-3c56b9150207" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a4f-7dd8-a1c8-68025883dbce" xlink:to="loc_us-gaap_StatementTable_019cdd48-2a4f-758b-8c42-3c56b9150207" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019cdd48-2a4f-758b-8c42-3c56b9150207" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-7808-a879-970775302776" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a4f-70cc-a7a4-e85b77f2bce6" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-7808-a879-970775302776" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2a4f-7afc-99dc-ca03c7f79961" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-7808-a879-970775302776" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2a4f-7afc-99dc-ca03c7f79961" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019cdd48-2a4f-752b-9385-174f6c03cc56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a4f-7808-a879-970775302776" xlink:to="loc_us-gaap_CommonClassBMember_019cdd48-2a4f-752b-9385-174f6c03cc56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a4f-7dd8-a1c8-68025883dbce" xlink:to="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateInvestmentPropertyNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Land_019cdd48-2a4f-78e4-a1d5-5cb3470871e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Land"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:to="loc_us-gaap_Land_019cdd48-2a4f-78e4-a1d5-5cb3470871e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBuildingAndBuildingImprovements_019cdd48-2a4f-75c8-b3c6-cb8d7ef51a4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentBuildingAndBuildingImprovements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:to="loc_us-gaap_InvestmentBuildingAndBuildingImprovements_019cdd48-2a4f-75c8-b3c6-cb8d7ef51a4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TenantImprovements_019cdd48-2a4f-721c-9768-04c3e51063e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TenantImprovements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:to="loc_us-gaap_TenantImprovements_019cdd48-2a4f-721c-9768-04c3e51063e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAtCost_019cdd48-2a4f-7c1f-bb03-017bf0647620" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateInvestmentPropertyAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyNetAbstract_019cdd48-2a4f-7ba3-85e2-7cb12d6be1c2" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAtCost_019cdd48-2a4f-7c1f-bb03-017bf0647620" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_019cdd48-2a4f-791d-ab54-67fbcf802957" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_019cdd48-2a4f-791d-ab54-67fbcf802957" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNet_019cdd48-2a4f-7522-b83c-8ebd30dca70b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateInvestmentPropertyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNet_019cdd48-2a4f-7522-b83c-8ebd30dca70b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentInLease_019cdd48-2a4f-7925-a987-0773ab5ffc48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentInLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:to="loc_us-gaap_NetInvestmentInLease_019cdd48-2a4f-7925-a987-0773ab5ffc48" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Investments_019cdd48-2a4f-73af-be9e-6c6d95079fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Investments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_019cdd48-2a4f-76a4-813f-79a376f305b8" xlink:to="loc_us-gaap_Investments_019cdd48-2a4f-73af-be9e-6c6d95079fd1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019cdd48-2a4f-770c-bc89-21103a714be3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019cdd48-2a4f-770c-bc89-21103a714be3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EscrowsAndReserves_019cdd48-2a4f-72fb-805b-cbf96c5120a2" xlink:href="pstl-20260331.xsd#pstl_EscrowsAndReserves"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_pstl_EscrowsAndReserves_019cdd48-2a4f-72fb-805b-cbf96c5120a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RentAndOtherReceivables_019cdd48-2a4f-7e10-82f8-46f89471c932" xlink:href="pstl-20260331.xsd#pstl_RentAndOtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_pstl_RentAndOtherReceivables_019cdd48-2a4f-7e10-82f8-46f89471c932" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssets_019cdd48-2a4f-790d-b060-948f182976fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssets_019cdd48-2a4f-790d-b060-948f182976fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsNet_019cdd48-2a4f-7b47-8ff0-745e377eab8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_OtherIntangibleAssetsNet_019cdd48-2a4f-7b47-8ff0-745e377eab8b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRentReceivablesNet_019cdd48-2a4f-7a14-b50c-d587c1bc4f49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredRentReceivablesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_DeferredRentReceivablesNet_019cdd48-2a4f-7a14-b50c-d587c1bc4f49" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2a4f-758a-93a7-3e6ea592efa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2a4f-758a-93a7-3e6ea592efa4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019cdd48-2a4f-741a-8ffd-6d251ad364cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019cdd48-2a4f-7f6d-9acd-b9eeee014d2f" xlink:to="loc_us-gaap_Assets_019cdd48-2a4f-741a-8ffd-6d251ad364cd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a4f-7dd8-a1c8-68025883dbce" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:to="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebt_019cdd48-2a4f-7c58-8c97-3a59947027a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_us-gaap_UnsecuredDebt_019cdd48-2a4f-7c58-8c97-3a59947027a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_019cdd48-2a4f-786b-8562-7f909b48d8a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LinesOfCreditCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_us-gaap_LinesOfCreditCurrent_019cdd48-2a4f-786b-8562-7f909b48d8a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_MortgageLevelDebt_019cdd48-2a4f-7d7b-86fb-e0844cdbf18d" xlink:href="pstl-20260331.xsd#pstl_MortgageLevelDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_pstl_MortgageLevelDebt_019cdd48-2a4f-7d7b-86fb-e0844cdbf18d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilities_019cdd48-2a4f-794c-8ee0-6773411f7eb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndOtherAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilities_019cdd48-2a4f-794c-8ee0-6773411f7eb2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2a4f-7cd4-b932-87128cc6e8cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2a4f-7cd4-b932-87128cc6e8cd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019cdd48-2a4f-7a4d-a204-e3cdb6937014" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019cdd48-2a4f-78ca-8962-78c4582d0205" xlink:to="loc_us-gaap_Liabilities_019cdd48-2a4f-7a4d-a204-e3cdb6937014" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019cdd48-2a4f-7772-9cf0-2660c0c96c5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019cdd48-2a4f-7772-9cf0-2660c0c96c5d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019cdd48-2a4f-762d-bdf0-2abab260a81a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_CommonStockValue_019cdd48-2a4f-762d-bdf0-2abab260a81a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019cdd48-2a4f-7ddc-8be3-de0781b89f78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019cdd48-2a4f-7ddc-8be3-de0781b89f78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019cdd48-2a4f-78f3-b48f-546f94294eec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019cdd48-2a4f-78f3-b48f-546f94294eec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019cdd48-2a4f-727d-8211-9cbfd795154d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019cdd48-2a4f-727d-8211-9cbfd795154d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019cdd48-2a4f-7628-98fb-6a48b464ec66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_StockholdersEquity_019cdd48-2a4f-7628-98fb-6a48b464ec66" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019cdd48-2a4f-7386-9217-88f39dce45eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_MinorityInterest_019cdd48-2a4f-7386-9217-88f39dce45eb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019cdd48-2a4f-77d3-a5a2-c679c9239344" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019cdd48-2a4f-7488-9db3-a340a30e3879" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019cdd48-2a4f-77d3-a5a2-c679c9239344" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019cdd48-2a4f-73f0-a1e5-eeef7894adc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019cdd48-2a4f-7dbe-8e14-8c16d02a7025" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019cdd48-2a4f-73f0-a1e5-eeef7894adc3" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="simple" xlink:href="pstl-20260331.xsd#ConsolidatedBalanceSheetsUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019cdd48-2a50-7691-b86a-c5e429ef9e1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:to="loc_us-gaap_StatementTable_019cdd48-2a50-7691-b86a-c5e429ef9e1c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-725d-8703-41a328c7f89c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019cdd48-2a50-7691-b86a-c5e429ef9e1c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-725d-8703-41a328c7f89c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-725d-8703-41a328c7f89c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-725d-8703-41a328c7f89c" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-725d-8703-41a328c7f89c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7371-9f6f-fbff7fe04400" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-725d-8703-41a328c7f89c" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7371-9f6f-fbff7fe04400" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2a50-7ec8-944f-b6c72bd2b576" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7371-9f6f-fbff7fe04400" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2a50-7ec8-944f-b6c72bd2b576" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019cdd48-2a50-7f8d-9aaa-77d2efd9da14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7371-9f6f-fbff7fe04400" xlink:to="loc_us-gaap_CommonClassBMember_019cdd48-2a50-7f8d-9aaa-77d2efd9da14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019cdd48-2a50-7f8d-acf7-dd3b587a7e20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019cdd48-2a50-7f8d-acf7-dd3b587a7e20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019cdd48-2a50-7d6d-9a17-d8cea552b2a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019cdd48-2a50-7d6d-9a17-d8cea552b2a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019cdd48-2a50-70cd-999e-bfc86e0ca690" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:to="loc_us-gaap_CommonStockSharesIssued_019cdd48-2a50-70cd-999e-bfc86e0ca690" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019cdd48-2a50-781b-bde9-1553ccc6b178" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-7109-af6a-b56ca37b2743" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019cdd48-2a50-781b-bde9-1553ccc6b178" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="simple" xlink:href="pstl-20260331.xsd#ConsolidatedStatementsofChangesinEquityUnaudited"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019cdd48-2a50-77d9-831b-bf6ce7677aa9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019cdd48-2a50-7248-9977-41197ff72cc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-77d9-831b-bf6ce7677aa9" xlink:to="loc_us-gaap_StatementTable_019cdd48-2a50-7248-9977-41197ff72cc8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2a50-7a92-bdf3-144bbd7a60fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019cdd48-2a50-7248-9977-41197ff72cc8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2a50-7a92-bdf3-144bbd7a60fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-7a92-bdf3-144bbd7a60fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2a50-7a92-bdf3-144bbd7a60fd" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-7a92-bdf3-144bbd7a60fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-700a-87ac-09bfdefa55f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2a50-7a92-bdf3-144bbd7a60fd" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-700a-87ac-09bfdefa55f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-700a-87ac-09bfdefa55f8" xlink:to="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019cdd48-2a50-74f9-b873-d44b9040515c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:to="loc_us-gaap_CommonStockMember_019cdd48-2a50-74f9-b873-d44b9040515c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019cdd48-2a50-72a1-8d68-04788dbd159d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019cdd48-2a50-72a1-8d68-04788dbd159d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cdd48-2a50-7b9a-8c51-3576ff18bd64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cdd48-2a50-7b9a-8c51-3576ff18bd64" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019cdd48-2a50-757a-bc84-8db7976a63c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019cdd48-2a50-7ffa-925a-ad0af738dbd1" xlink:to="loc_us-gaap_RetainedEarningsMember_019cdd48-2a50-757a-bc84-8db7976a63c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2a50-7e20-b16c-6519699ff85e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cdd48-2a50-700a-87ac-09bfdefa55f8" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2a50-7e20-b16c-6519699ff85e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cdd48-2a50-77d9-831b-bf6ce7677aa9" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019cdd48-2a50-71bc-b0c6-3ddf986afcc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_SharesOutstanding_019cdd48-2a50-71bc-b0c6-3ddf986afcc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019cdd48-2a50-72ae-baa7-5a952538bef9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019cdd48-2a50-72ae-baa7-5a952538bef9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019cdd48-2a50-7092-8fa8-2af4598d860c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019cdd48-2a50-7092-8fa8-2af4598d860c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019cdd48-2a50-707d-a387-2f983c93dd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019cdd48-2a50-707d-a387-2f983c93dd1f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_019dd9cd-1423-78ba-8a70-f5381bffc65c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_019dd9cd-1423-78ba-8a70-f5381bffc65c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockIssuedDuringPeriodSharesRedemptionOfNoncontrollingInterests_019dd9d7-d1a2-7fb5-a9c6-55c42a1788e0" xlink:href="pstl-20260331.xsd#pstl_StockIssuedDuringPeriodSharesRedemptionOfNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_pstl_StockIssuedDuringPeriodSharesRedemptionOfNoncontrollingInterests_019dd9d7-d1a2-7fb5-a9c6-55c42a1788e0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockIssuedDuringPeriodValueRedemptionOfNoncontrollingInterests_019dd9d7-f714-741a-aac1-c7ef9dd9bbc3" xlink:href="pstl-20260331.xsd#pstl_StockIssuedDuringPeriodValueRedemptionOfNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_pstl_StockIssuedDuringPeriodValueRedemptionOfNoncontrollingInterests_019dd9d7-f714-741a-aac1-c7ef9dd9bbc3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019cdd48-2a50-7578-8df0-86bbc95529f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019cdd48-2a50-7578-8df0-86bbc95529f2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019cdd48-2a50-7097-a118-bb615d96a89f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019cdd48-2a50-7097-a118-bb615d96a89f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019cdd48-2a50-76fc-9593-c768465717c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019cdd48-2a50-76fc-9593-c768465717c9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition_019cdd48-2a50-7cc2-a318-e6865297f17b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition_019cdd48-2a50-7cc2-a318-e6865297f17b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019dd9d1-d8b8-7ea9-9d3e-a27fba0c6654" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019dd9d1-d8b8-7ea9-9d3e-a27fba0c6654" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings_019cdd48-2a50-718e-bcca-5052ee4b2b64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings_019cdd48-2a50-718e-bcca-5052ee4b2b64" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_019cdd48-2a50-7feb-91e8-8ddddcfabfa3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_DividendsCommonStockCash_019cdd48-2a50-7feb-91e8-8ddddcfabfa3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019cdd48-2a50-7097-9fa9-1f693697eae4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019cdd48-2a50-7097-9fa9-1f693697eae4" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019cdd48-2a50-788b-8316-f9b5bd0b40fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_us-gaap_ProfitLoss_019cdd48-2a50-788b-8316-f9b5bd0b40fb" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ReallocationOfNoncontrollingInterest_019cdd48-2a50-7da9-861e-0be1c45550a9" xlink:href="pstl-20260331.xsd#pstl_ReallocationOfNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cdd48-2a50-7eee-8154-76ea038792a2" xlink:to="loc_pstl_ReallocationOfNoncontrollingInterest_019cdd48-2a50-7da9-861e-0be1c45550a9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019cdd48-2a50-7fb8-8672-17b3f0280ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019cdd48-2a50-7262-902c-9b6a625e8916" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/OrganizationandDescriptionofBusinessNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#OrganizationandDescriptionofBusinessNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/OrganizationandDescriptionofBusinessNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:href="pstl-20260331.xsd#pstl_OrganizationandDescriptionofBusinessDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-760d-814d-4b9157b2408b" xlink:href="pstl-20260331.xsd#pstl_OrganizationAndDescriptionOfBusinessTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-760d-814d-4b9157b2408b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2a50-719b-913f-a20cac1c7183" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-760d-814d-4b9157b2408b" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2a50-719b-913f-a20cac1c7183" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2a50-719b-913f-a20cac1c7183_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2a50-719b-913f-a20cac1c7183" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2a50-719b-913f-a20cac1c7183_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2a50-7960-8fc8-505912fae946" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2a50-719b-913f-a20cac1c7183" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2a50-7960-8fc8-505912fae946" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_019cdd48-2a50-7c26-80a8-b4ac91296dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2a50-7960-8fc8-505912fae946" xlink:to="loc_us-gaap_IPOMember_019cdd48-2a50-7c26-80a8-b4ac91296dc6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019cdd48-2a50-7558-a655-3dba15003898" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-760d-814d-4b9157b2408b" xlink:to="loc_dei_LegalEntityAxis_019cdd48-2a50-7558-a655-3dba15003898" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2a50-7558-a655-3dba15003898_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2a50-7558-a655-3dba15003898" xlink:to="loc_dei_EntityDomain_019cdd48-2a50-7558-a655-3dba15003898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2a50-7efa-b809-a48af2ef35fa" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2a50-7558-a655-3dba15003898" xlink:to="loc_dei_EntityDomain_019cdd48-2a50-7efa-b809-a48af2ef35fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_UnitedStatesPostalServiceMember_019cdd48-2a50-70d9-bbe3-7d0532d16176" xlink:href="pstl-20260331.xsd#pstl_UnitedStatesPostalServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019cdd48-2a50-7efa-b809-a48af2ef35fa" xlink:to="loc_pstl_UnitedStatesPostalServiceMember_019cdd48-2a50-70d9-bbe3-7d0532d16176" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2a50-7aed-b98e-881bf012d6d8" xlink:href="pstl-20260331.xsd#pstl_RealEstateAssetCounselingLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019cdd48-2a50-7efa-b809-a48af2ef35fa" xlink:to="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2a50-7aed-b98e-881bf012d6d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-7b45-ac61-93f8e555d008" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-760d-814d-4b9157b2408b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-7b45-ac61-93f8e555d008" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7b45-ac61-93f8e555d008_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-7b45-ac61-93f8e555d008" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-7b45-ac61-93f8e555d008_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-782c-ad68-82411ef30b33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2a50-7b45-ac61-93f8e555d008" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-782c-ad68-82411ef30b33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2a50-766e-afcf-9fe5422294b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-782c-ad68-82411ef30b33" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2a50-766e-afcf-9fe5422294b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019cdd48-2a50-799e-8675-d158ef21359d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2a50-782c-ad68-82411ef30b33" xlink:to="loc_us-gaap_CommonClassBMember_019cdd48-2a50-799e-8675-d158ef21359d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019cdd48-2a50-78a3-b57f-7c1deb832555" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019cdd48-2a50-78a3-b57f-7c1deb832555" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PercentageOfInterestInOperatingPartnership_019cdd48-2a50-77c2-bc1a-e4863029073b" xlink:href="pstl-20260331.xsd#pstl_PercentageOfInterestInOperatingPartnership"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_pstl_PercentageOfInterestInOperatingPartnership_019cdd48-2a50-77c2-bc1a-e4863029073b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfRealEstateProperties_019cdd48-2a50-7412-8dd9-232ea0f92150" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfRealEstateProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_NumberOfRealEstateProperties_019cdd48-2a50-7412-8dd9-232ea0f92150" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfStatesInWhichEntityOperates_019cdd48-2a50-7803-ae1f-6d9c202c7ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfStatesInWhichEntityOperates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_NumberOfStatesInWhichEntityOperates_019cdd48-2a50-7803-ae1f-6d9c202c7ce4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019cdd48-2a50-78f3-aaa5-75c758fc4f63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019cdd48-2a50-78f3-aaa5-75c758fc4f63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019cdd48-2a50-7ed4-a2b2-89291b5a1a36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_CommonStockSharesIssued_019cdd48-2a50-7ed4-a2b2-89291b5a1a36" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019cdd48-2a50-757d-9e60-f7ff0ccb24ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationandDescriptionofBusinessDetailsLineItems_019cdd48-2a50-7ce3-985e-eb7da05d965e" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019cdd48-2a50-757d-9e60-f7ff0ccb24ce" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:href="pstl-20260331.xsd#pstl_OrganizationAndDescriptionOfBusinessLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:href="pstl-20260331.xsd#pstl_OrganizationAndDescriptionOfBusinessTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2a50-7ec2-afd9-eb586b0447ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2a50-7ec2-afd9-eb586b0447ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2a50-7ec2-afd9-eb586b0447ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2a50-7ec2-afd9-eb586b0447ce" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2a50-7ec2-afd9-eb586b0447ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2a50-78c6-ab6e-e6ee20fc755c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2a50-7ec2-afd9-eb586b0447ce" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2a50-78c6-ab6e-e6ee20fc755c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019cdd48-2a50-7fd0-b319-7678a66ea51f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2a50-78c6-ab6e-e6ee20fc755c" xlink:to="loc_us-gaap_InterestRateSwapMember_019cdd48-2a50-7fd0-b319-7678a66ea51f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cdd48-2a50-7b88-9332-333cdc09c9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cdd48-2a50-7b88-9332-333cdc09c9ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cdd48-2a50-7b88-9332-333cdc09c9ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cdd48-2a50-7b88-9332-333cdc09c9ff" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cdd48-2a50-7b88-9332-333cdc09c9ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cdd48-2a50-73b9-8041-e7b047ebe5b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cdd48-2a50-7b88-9332-333cdc09c9ff" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cdd48-2a50-73b9-8041-e7b047ebe5b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019cdd48-2a50-7a81-aca2-7e63b24245f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cdd48-2a50-73b9-8041-e7b047ebe5b9" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019cdd48-2a50-7a81-aca2-7e63b24245f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-7cd3-aab4-853d260eab2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019cdd48-2a50-79ce-a2d7-08d4b2edcbf0" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-7cd3-aab4-853d260eab2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019cdd48-2a50-72fc-8ff0-42c19a8349c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-7cd3-aab4-853d260eab2e" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019cdd48-2a50-72fc-8ff0-42c19a8349c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_MeasurementInputTerminalCapitalizationRateMember_019cdd48-2a50-795c-8802-a13278deb064" xlink:href="pstl-20260331.xsd#pstl_MeasurementInputTerminalCapitalizationRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019cdd48-2a50-7cd3-aab4-853d260eab2e" xlink:to="loc_pstl_MeasurementInputTerminalCapitalizationRateMember_019cdd48-2a50-795c-8802-a13278deb064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019cdd48-2a50-7539-9c6d-a95044eda7ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019cdd48-2a50-7539-9c6d-a95044eda7ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cdd48-2a50-7539-9c6d-a95044eda7ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cdd48-2a50-7539-9c6d-a95044eda7ca" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cdd48-2a50-7539-9c6d-a95044eda7ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cdd48-2a50-7037-8522-2701a9739b65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cdd48-2a50-7539-9c6d-a95044eda7ca" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cdd48-2a50-7037-8522-2701a9739b65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019cdd48-2a50-7072-86e0-51fad2de4f1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019cdd48-2a50-7037-8522-2701a9739b65" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019cdd48-2a50-7072-86e0-51fad2de4f1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cdd48-2a50-7c6c-a0dd-b87de5e9c760" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cdd48-2a50-7c6c-a0dd-b87de5e9c760" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cdd48-2a50-7c6c-a0dd-b87de5e9c760_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cdd48-2a50-7c6c-a0dd-b87de5e9c760" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cdd48-2a50-7c6c-a0dd-b87de5e9c760_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cdd48-2a50-712c-9bee-39733fdc2ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cdd48-2a50-7c6c-a0dd-b87de5e9c760" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cdd48-2a50-712c-9bee-39733fdc2ddf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019cdd48-2a50-70da-887d-7d82d53465ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cdd48-2a50-712c-9bee-39733fdc2ddf" xlink:to="loc_us-gaap_SalesRevenueNetMember_019cdd48-2a50-70da-887d-7d82d53465ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019cdd48-2a50-7a76-9f11-5ac80a62d295" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessTable_019cdd48-2a50-713d-8aca-cf4251a1ef84" xlink:to="loc_srt_StatementGeographicalAxis_019cdd48-2a50-7a76-9f11-5ac80a62d295" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019cdd48-2a50-7a76-9f11-5ac80a62d295_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019cdd48-2a50-7a76-9f11-5ac80a62d295" xlink:to="loc_srt_SegmentGeographicalDomain_019cdd48-2a50-7a76-9f11-5ac80a62d295_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019cdd48-2a50-741b-add0-5039fa13e901" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019cdd48-2a50-7a76-9f11-5ac80a62d295" xlink:to="loc_srt_SegmentGeographicalDomain_019cdd48-2a50-741b-add0-5039fa13e901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_PA_019cdd48-2a50-71b6-8954-2f4548026508" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_PA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019cdd48-2a50-741b-add0-5039fa13e901" xlink:to="loc_stpr_PA_019cdd48-2a50-71b6-8954-2f4548026508" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019cdd48-2a50-7747-98b2-16bad1e4f590" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019cdd48-2a50-7747-98b2-16bad1e4f590" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableFairValueDisclosure_019cdd48-2a50-79f6-bb82-905694e986da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_LoansPayableFairValueDisclosure_019cdd48-2a50-79f6-bb82-905694e986da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtCurrent_019cdd48-2a50-7b56-8032-7a075b9a3442" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_SecuredDebtCurrent_019cdd48-2a50-7b56-8032-7a075b9a3442" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019cdd48-2a50-741d-bb24-2e383452d31b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_DerivativeAssets_019cdd48-2a50-741d-bb24-2e383452d31b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019cdd48-2a50-720a-a924-febc7c6f234b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_DerivativeLiabilities_019cdd48-2a50-720a-a924-febc7c6f234b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesHeldForSale_019cdd48-2a50-72cf-bd0d-b13e06b451dc" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_pstl_NumberOfPropertiesHeldForSale_019cdd48-2a50-72cf-bd0d-b13e06b451dc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesRemeasured_019cdd48-2a50-74e9-9459-117849a9959c" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesRemeasured"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_pstl_NumberOfPropertiesRemeasured_019cdd48-2a50-74e9-9459-117849a9959c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RealEstateMeasurementInput_019cdd48-2a50-71b8-99be-70fdae436906" xlink:href="pstl-20260331.xsd#pstl_RealEstateMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_pstl_RealEstateMeasurementInput_019cdd48-2a50-71b8-99be-70fdae436906" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfRealEstate_019cdd48-2a50-775c-acd7-1587e7d43a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_ImpairmentOfRealEstate_019cdd48-2a50-775c-acd7-1587e7d43a5b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019cdd48-2a50-76d2-9ffc-91759fe67cfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019cdd48-2a50-76d2-9ffc-91759fe67cfa" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019cdd48-2a50-7092-bc72-f25f86e59fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019cdd48-2a50-7092-bc72-f25f86e59fa1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019cdd48-2a50-7225-b32d-834c30602e01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OrganizationAndDescriptionOfBusinessLineItems_019cdd48-2a50-7871-bdeb-20a5814c8a77" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019cdd48-2a50-7225-b32d-834c30602e01" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/RealEstateTransactionsNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#RealEstateTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/RealEstateTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019debb9-ccbf-77bb-84a1-6ce7020ade74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019debb9-ccbf-77bb-84a1-6ce7020ade74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019debb9-ccbf-77bb-84a1-6ce7020ade74_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019debb9-ccbf-77bb-84a1-6ce7020ade74" xlink:to="loc_us-gaap_RelatedPartyDomain_019debb9-ccbf-77bb-84a1-6ce7020ade74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019debb9-ccbf-788e-8140-c44b8385b223" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019debb9-ccbf-77bb-84a1-6ce7020ade74" xlink:to="loc_us-gaap_RelatedPartyDomain_019debb9-ccbf-788e-8140-c44b8385b223" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019debba-4fec-797f-b31f-d2c41fc8462e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019debb9-ccbf-788e-8140-c44b8385b223" xlink:to="loc_us-gaap_RelatedPartyMember_019debba-4fec-797f-b31f-d2c41fc8462e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019debfc-2b2e-7575-b58f-94964cfe87ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019debfc-2b2e-7575-b58f-94964cfe87ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019debfc-2b2e-7575-b58f-94964cfe87ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019debfc-2b2e-7575-b58f-94964cfe87ff" xlink:to="loc_us-gaap_ClassOfStockDomain_019debfc-2b2e-7575-b58f-94964cfe87ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019debfc-2b2e-76aa-9c20-ce1f3f5e3d5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019debfc-2b2e-7575-b58f-94964cfe87ff" xlink:to="loc_us-gaap_ClassOfStockDomain_019debfc-2b2e-76aa-9c20-ce1f3f5e3d5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019debfc-2b2e-79e7-9e8f-3b9f0306980b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019debfc-2b2e-76aa-9c20-ce1f3f5e3d5a" xlink:to="loc_us-gaap_CommonClassAMember_019debfc-2b2e-79e7-9e8f-3b9f0306980b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cdd48-2a50-73b2-a58c-f2f4aa18e210" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cdd48-2a50-73b2-a58c-f2f4aa18e210" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-73b2-a58c-f2f4aa18e210_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cdd48-2a50-73b2-a58c-f2f4aa18e210" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-73b2-a58c-f2f4aa18e210_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-722b-8792-eae41844d32f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cdd48-2a50-73b2-a58c-f2f4aa18e210" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-722b-8792-eae41844d32f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_019debc2-9df0-7e9f-8595-b1f3975a4af2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-722b-8792-eae41844d32f" xlink:to="loc_us-gaap_LandMember_019debc2-9df0-7e9f-8595-b1f3975a4af2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_019debfd-c267-70d7-8ffd-60d2afe1bbf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cdd48-2a50-722b-8792-eae41844d32f" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_019debfd-c267-70d7-8ffd-60d2afe1bbf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019debc2-6211-75cc-abb3-6c53898a9091" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019debc2-6211-75cc-abb3-6c53898a9091" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-75cc-abb3-6c53898a9091_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019debc2-6211-75cc-abb3-6c53898a9091" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-75cc-abb3-6c53898a9091_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-7e36-bf3b-a582c462ed24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019debc2-6211-75cc-abb3-6c53898a9091" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-7e36-bf3b-a582c462ed24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InPlaceLeaseIntangiblesMember_019debfc-9b1b-7285-a3d9-8ca775427a63" xlink:href="pstl-20260331.xsd#pstl_InPlaceLeaseIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-7e36-bf3b-a582c462ed24" xlink:to="loc_pstl_InPlaceLeaseIntangiblesMember_019debfc-9b1b-7285-a3d9-8ca775427a63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_BelowMarketLeasesMember_019debc2-70fd-7f8e-9fc2-d6f9c6379504" xlink:href="pstl-20260331.xsd#pstl_BelowMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019debc2-6211-7e36-bf3b-a582c462ed24" xlink:to="loc_pstl_BelowMarketLeasesMember_019debc2-70fd-7f8e-9fc2-d6f9c6379504" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassAxis_019debfc-c80e-702e-be58-26b6018a4b0c" xlink:href="pstl-20260331.xsd#pstl_FiniteLivedIntangibleLiabilitiesByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassAxis_019debfc-c80e-702e-be58-26b6018a4b0c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80e-702e-be58-26b6018a4b0c_default" xlink:href="pstl-20260331.xsd#pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassAxis_019debfc-c80e-702e-be58-26b6018a4b0c" xlink:to="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80e-702e-be58-26b6018a4b0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80f-7c32-bbf0-a880539495cc" xlink:href="pstl-20260331.xsd#pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassAxis_019debfc-c80e-702e-be58-26b6018a4b0c" xlink:to="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80f-7c32-bbf0-a880539495cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_BelowMarketLeasesMember_019debfc-c80f-75d7-868b-0ba665d14955" xlink:href="pstl-20260331.xsd#pstl_BelowMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80f-7c32-bbf0-a880539495cc" xlink:to="loc_pstl_BelowMarketLeasesMember_019debfc-c80f-75d7-868b-0ba665d14955" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OperatingLeaseWithPurchaseOptionsMember_019debfc-ec11-79d9-b126-5d664c79e8d2" xlink:href="pstl-20260331.xsd#pstl_OperatingLeaseWithPurchaseOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_FiniteLivedIntangibleLiabilitiesByMajorClassDomain_019debfc-c80f-7c32-bbf0-a880539495cc" xlink:to="loc_pstl_OperatingLeaseWithPurchaseOptionsMember_019debfc-ec11-79d9-b126-5d664c79e8d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_019cdd48-2a50-7f2a-9f92-4df6e87ac4c0" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019cdd48-2a50-7b36-9b44-c17e170c47e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019cdd48-2a50-7b1c-8cf0-8816b6c7d4e6" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019cdd48-2a50-7b36-9b44-c17e170c47e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PropertiesDamagedAndRelatedRepairsMember_019cdd48-2a50-7ced-81ff-b87420ced726" xlink:href="pstl-20260331.xsd#pstl_PropertiesDamagedAndRelatedRepairsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019cdd48-2a50-7b36-9b44-c17e170c47e4" xlink:to="loc_pstl_PropertiesDamagedAndRelatedRepairsMember_019cdd48-2a50-7ced-81ff-b87420ced726" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesAcquired_019debb9-a6ee-7783-9a11-6803007e8cc3" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_pstl_NumberOfPropertiesAcquired_019debb9-a6ee-7783-9a11-6803007e8cc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireRealEstate_019debfb-c32e-7e9c-9ff7-07187828af97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_us-gaap_PaymentsToAcquireRealEstate_019debfb-c32e-7e9c-9ff7-07187828af97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RealEstateInvestmentPropertyAcquiredAtCost_019debfb-e91b-7ebc-96e0-2efb96c0eacd" xlink:href="pstl-20260331.xsd#pstl_RealEstateInvestmentPropertyAcquiredAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_pstl_RealEstateInvestmentPropertyAcquiredAtCost_019debfb-e91b-7ebc-96e0-2efb96c0eacd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PurchasePriceOfPostalPortfolioAcquiredIncludingClosingCosts_019debfc-2b2e-7f4c-aa0a-f181f8475c9d" xlink:href="pstl-20260331.xsd#pstl_PurchasePriceOfPostalPortfolioAcquiredIncludingClosingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_pstl_PurchasePriceOfPostalPortfolioAcquiredIncludingClosingCosts_019debfc-2b2e-7f4c-aa0a-f181f8475c9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualProvision_019cdd48-2a50-7b8f-ba47-e9151131d2c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyAccrualProvision"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_us-gaap_LossContingencyAccrualProvision_019cdd48-2a50-7b8f-ba47-e9151131d2c6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyRelatedReceivableCarryingValueAdditions_019cdd48-2a50-74c7-94d8-dcde1da70cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyRelatedReceivableCarryingValueAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_us-gaap_LossContingencyRelatedReceivableCarryingValueAdditions_019cdd48-2a50-74c7-94d8-dcde1da70cd4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyReceivable_019def52-b21c-7d5a-8ce1-910ae450a0a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_us-gaap_LossContingencyReceivable_019def52-b21c-7d5a-8ce1-910ae450a0a2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_CasualtyAndImpairmentLossesNet_019cdd48-2a50-7297-adba-20128584e1b9" xlink:href="pstl-20260331.xsd#pstl_CasualtyAndImpairmentLossesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_pstl_CasualtyAndImpairmentLossesNet_019cdd48-2a50-7297-adba-20128584e1b9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesDamaged_019def53-ca78-7e21-9f53-adbb82b6681d" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesDamaged"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_019cdd48-2a50-7a62-acbd-b37cff6ff1f4" xlink:to="loc_pstl_NumberOfPropertiesDamaged_019def53-ca78-7e21-9f53-adbb82b6681d" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/IntangibleAssetsandLiabilitiesScheduleofintangibleassetsandliabilitiesDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#IntangibleAssetsandLiabilitiesScheduleofintangibleassetsandliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/IntangibleAssetsandLiabilitiesScheduleofintangibleassetsandliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:href="pstl-20260331.xsd#pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleofintangibleassetsandliabilitiesTable_019cdd48-2a50-74b9-ae10-b9f79b759962" xlink:href="pstl-20260331.xsd#pstl_IntangibleAssetsandLiabilitiesDetailsScheduleofintangibleassetsandliabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleofintangibleassetsandliabilitiesTable_019cdd48-2a50-74b9-ae10-b9f79b759962" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2a50-7870-a0bd-64a9eb9cca34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleofintangibleassetsandliabilitiesTable_019cdd48-2a50-74b9-ae10-b9f79b759962" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2a50-7870-a0bd-64a9eb9cca34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7870-a0bd-64a9eb9cca34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2a50-7870-a0bd-64a9eb9cca34" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7870-a0bd-64a9eb9cca34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7916-8c0f-68f29996ae7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2a50-7870-a0bd-64a9eb9cca34" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7916-8c0f-68f29996ae7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InPlaceLeaseIntangiblesMember_019cdd48-2a50-757e-9dca-6b640af8005b" xlink:href="pstl-20260331.xsd#pstl_InPlaceLeaseIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7916-8c0f-68f29996ae7d" xlink:to="loc_pstl_InPlaceLeaseIntangiblesMember_019cdd48-2a50-757e-9dca-6b640af8005b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AboveMarketLeasesMember_019cdd48-2a50-7468-b0e7-6de7fd380ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AboveMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2a50-7916-8c0f-68f29996ae7d" xlink:to="loc_us-gaap_AboveMarketLeasesMember_019cdd48-2a50-7468-b0e7-6de7fd380ec8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019cdd48-2a50-7aa9-85b8-c8c83a97e422" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019cdd48-2a50-7aa9-85b8-c8c83a97e422" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesGross_019cdd48-2a50-7015-b9e6-ff08ea95cc49" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_pstl_OtherIntangibleLiabilitiesGross_019cdd48-2a50-7015-b9e6-ff08ea95cc49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseGross_019cdd48-2a50-75ae-84d1-feee65ee7b97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_BelowMarketLeaseGross_019cdd48-2a50-75ae-84d1-feee65ee7b97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019cdd48-2a50-7688-9f51-8038df92fe5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019cdd48-2a50-7688-9f51-8038df92fe5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesAccumulatedAmortization_019cdd48-2a50-7118-9371-6686ac489ca8" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_pstl_OtherIntangibleLiabilitiesAccumulatedAmortization_019cdd48-2a50-7118-9371-6686ac489ca8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAccumulatedAmortization_019cdd48-2a50-79aa-94e0-cb0f9d92baa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_BelowMarketLeaseAccumulatedAmortization_019cdd48-2a50-79aa-94e0-cb0f9d92baa7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2a50-7d0f-87dc-a5372964f4c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2a50-7d0f-87dc-a5372964f4c4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesNet_019cdd48-2a50-7a28-ad87-48d7a57f1aec" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_pstl_OtherIntangibleLiabilitiesNet_019cdd48-2a50-7a28-ad87-48d7a57f1aec" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2a50-77de-b998-85a2a1ed06bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsAndLiabilitiesDetailsScheduleOfIntangibleAssetsAndLiabilitiesLineItems_019cdd48-2a50-7d1f-9e7d-efb3bcac59ea" xlink:to="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2a50-77de-b998-85a2a1ed06bf" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/IntangibleAssetsandLiabilitiesScheduleoffutureamortizationDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#IntangibleAssetsandLiabilitiesScheduleoffutureamortizationDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/IntangibleAssetsandLiabilitiesScheduleoffutureamortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems_019cdd48-2b36-7e33-aae0-965f5555bd30" xlink:href="pstl-20260331.xsd#pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationTable_019cdd48-2b36-7583-988b-879d97489515" xlink:href="pstl-20260331.xsd#pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems_019cdd48-2b36-7e33-aae0-965f5555bd30" xlink:to="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationTable_019cdd48-2b36-7583-988b-879d97489515" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2b36-7340-8714-c4482b9e51e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationTable_019cdd48-2b36-7583-988b-879d97489515" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2b36-7340-8714-c4482b9e51e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-7340-8714-c4482b9e51e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2b36-7340-8714-c4482b9e51e3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-7340-8714-c4482b9e51e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-75b6-b44a-b0e8ec063586" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdd48-2b36-7340-8714-c4482b9e51e3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-75b6-b44a-b0e8ec063586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InPlaceLeaseIntangiblesMember_019cdd48-2b36-77ef-a223-617d4a0b3c27" xlink:href="pstl-20260331.xsd#pstl_InPlaceLeaseIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-75b6-b44a-b0e8ec063586" xlink:to="loc_pstl_InPlaceLeaseIntangiblesMember_019cdd48-2b36-77ef-a223-617d4a0b3c27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AboveMarketLeasesMember_019cdd48-2b36-712b-a835-a9286cdc7c06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AboveMarketLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdd48-2b36-75b6-b44a-b0e8ec063586" xlink:to="loc_us-gaap_AboveMarketLeasesMember_019cdd48-2b36-712b-a835-a9286cdc7c06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems_019cdd48-2b36-7e33-aae0-965f5555bd30" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019cdd48-2b36-7b61-9701-ba6fb802bed5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019cdd48-2b36-7b61-9701-ba6fb802bed5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019cdd48-2b36-75f2-b16c-7f444bc5f34f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019cdd48-2b36-75f2-b16c-7f444bc5f34f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019cdd48-2b36-7437-9449-7305f4ff826d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019cdd48-2b36-7437-9449-7305f4ff826d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019cdd48-2b36-7332-a97f-e14d3ce795c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019cdd48-2b36-7332-a97f-e14d3ce795c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019cdd48-2b36-7492-8aae-daa0bb9eac80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019cdd48-2b36-7492-8aae-daa0bb9eac80" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019cdd48-2b36-7706-a8d8-0c4cfb3cf6b0" xlink:href="pstl-20260331.xsd#pstl_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_pstl_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019cdd48-2b36-7706-a8d8-0c4cfb3cf6b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2b36-7f6d-9ae5-bac131a068d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseCurrentAndFiveSucceedingFiscalYearsAbstract_019cdd48-2b36-74eb-90a7-9c76ec2b7dca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cdd48-2b36-7f6d-9ae5-bac131a068d4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems_019cdd48-2b36-7e33-aae0-965f5555bd30" xlink:to="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationRemainderOfFiscalYear_019cdd48-2b36-7211-b869-38406da96793" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationRemainderOfFiscalYear_019cdd48-2b36-7211-b869-38406da96793" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearOne_019cdd48-2b36-7678-bac5-8c4bc694e1c6" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearOne_019cdd48-2b36-7678-bac5-8c4bc694e1c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearTwo_019cdd48-2b36-72a1-97eb-f81de0eec259" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearTwo_019cdd48-2b36-72a1-97eb-f81de0eec259" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearThree_019cdd48-2b36-7877-beb6-f422f1e9f0f1" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearThree_019cdd48-2b36-7877-beb6-f422f1e9f0f1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearFour_019cdd48-2b36-7faa-9cd8-822da156f09b" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationYearFour_019cdd48-2b36-7faa-9cd8-822da156f09b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationAfterYearFour_019cdd48-2b36-7af3-9a79-5b5f6972be1c" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesExpectedAmortizationAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesExpectedAmortizationAfterYearFour_019cdd48-2b36-7af3-9a79-5b5f6972be1c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OtherIntangibleLiabilitiesNet_019cdd48-2b36-75bd-bcae-94446804945a" xlink:href="pstl-20260331.xsd#pstl_OtherIntangibleLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_OtherIntangibleLiabilitiesMaturityAbstract_019cdd48-2b36-75d1-914e-5bb86fdca39d" xlink:to="loc_pstl_OtherIntangibleLiabilitiesNet_019cdd48-2b36-75bd-bcae-94446804945a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_IntangibleAssetsandLiabilitiesDetailsScheduleoffutureamortizationLineItems_019cdd48-2b36-7e33-aae0-965f5555bd30" xlink:to="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAmortizationIncomeRemainderOfFiscalYear_019cdd48-2b36-7020-8988-8059aa952c7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAmortizationIncomeRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseAmortizationIncomeRemainderOfFiscalYear_019cdd48-2b36-7020-8988-8059aa952c7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAmortizationIncomeNextTwelveMonths_019cdd48-2b36-788a-a4d5-8a4f9e0e7476" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAmortizationIncomeNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseAmortizationIncomeNextTwelveMonths_019cdd48-2b36-788a-a4d5-8a4f9e0e7476" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearTwo_019cdd48-2b36-7d87-b44a-2a677db6b5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAmortizationIncomeYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearTwo_019cdd48-2b36-7d87-b44a-2a677db6b5d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearThree_019cdd48-2b36-7029-867b-1d717ef0b9b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAmortizationIncomeYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearThree_019cdd48-2b36-7029-867b-1d717ef0b9b8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearFour_019cdd48-2b36-7eb1-8aee-ac65c06e2b47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseAmortizationIncomeYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseAmortizationIncomeYearFour_019cdd48-2b36-7eb1-8aee-ac65c06e2b47" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_BelowMarketLeaseAmortizationIncomeAfterYearFour_019cdd48-2b36-7450-8c4e-063a423867c0" xlink:href="pstl-20260331.xsd#pstl_BelowMarketLeaseAmortizationIncomeAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_pstl_BelowMarketLeaseAmortizationIncomeAfterYearFour_019cdd48-2b36-7450-8c4e-063a423867c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2b36-7ef4-bf23-0967dd098671" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BelowMarketLeaseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BelowMarketLeaseAbstract_019cdd48-2b36-7033-9b9f-8d8446450254" xlink:to="loc_us-gaap_BelowMarketLeaseNet_019cdd48-2b36-7ef4-bf23-0967dd098671" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/DebtScheduleofprincipalbalancesofmortgageloanspayableDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#DebtScheduleofprincipalbalancesofmortgageloanspayableDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/DebtScheduleofprincipalbalancesofmortgageloanspayableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-72c0-ad4c-36995d318256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-72c0-ad4c-36995d318256" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7c5f-957c-936aa464e8ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-72c0-ad4c-36995d318256" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7c5f-957c-936aa464e8ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7c5f-957c-936aa464e8ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7c5f-957c-936aa464e8ee" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7c5f-957c-936aa464e8ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7a11-9c48-3b2705700f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7c5f-957c-936aa464e8ee" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7a11-9c48-3b2705700f9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019cdd48-2b36-7196-8c2f-8fd033c6170e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7a11-9c48-3b2705700f9f" xlink:to="loc_us-gaap_LineOfCreditMember_019cdd48-2b36-7196-8c2f-8fd033c6170e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7f91-87d4-7f0246b375a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7a11-9c48-3b2705700f9f" xlink:to="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7f91-87d4-7f0246b375a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-72f4-ae4a-13d247ba478b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-72c0-ad4c-36995d318256" xlink:to="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-72f4-ae4a-13d247ba478b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-72f4-ae4a-13d247ba478b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-72f4-ae4a-13d247ba478b" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-72f4-ae4a-13d247ba478b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-78ae-82d1-70b5a2320c45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-72f4-ae4a-13d247ba478b" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-78ae-82d1-70b5a2320c45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-7e6b-a572-fe48077a85aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-78ae-82d1-70b5a2320c45" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-7e6b-a572-fe48077a85aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-7bf8-b9f0-c16de60d189e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-72c0-ad4c-36995d318256" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-7bf8-b9f0-c16de60d189e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bf8-b9f0-c16de60d189e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-7bf8-b9f0-c16de60d189e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bf8-b9f0-c16de60d189e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-7bf8-b9f0-c16de60d189e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_TwentyTwentyOneRevolvingCreditFacilityMember_019cdd48-2b36-76c2-8e14-58c5984f4bc0" xlink:href="pstl-20260331.xsd#pstl_TwentyTwentyOneRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_TwentyTwentyOneRevolvingCreditFacilityMember_019cdd48-2b36-76c2-8e14-58c5984f4bc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2021TermLoanMember_019cdd48-2b36-7140-9b1d-e50c3da9a006" xlink:href="pstl-20260331.xsd#pstl_A2021TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_A2021TermLoanMember_019cdd48-2b36-7140-9b1d-e50c3da9a006" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_VisionBankMember_019cdd48-2b36-72ea-9d0a-86245ddfebf2" xlink:href="pstl-20260331.xsd#pstl_VisionBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_VisionBankMember_019cdd48-2b36-72ea-9d0a-86245ddfebf2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7fad-8511-cb5fd8a72444" xlink:href="pstl-20260331.xsd#pstl_FirstOklahomaBankLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7fad-8511-cb5fd8a72444" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_VisionBankTwoThousandEighteenMember_019cdd48-2b36-7de6-8d54-b1354fd402bf" xlink:href="pstl-20260331.xsd#pstl_VisionBankTwoThousandEighteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_VisionBankTwoThousandEighteenMember_019cdd48-2b36-7de6-8d54-b1354fd402bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AIGTwoThousandAndTwentyDecemberMember_019cdd48-2b36-77a6-bc8a-29fc132725c4" xlink:href="pstl-20260331.xsd#pstl_AIGTwoThousandAndTwentyDecemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_AIGTwoThousandAndTwentyDecemberMember_019cdd48-2b36-77a6-bc8a-29fc132725c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SellerFinancing2024Member_019cdd48-2b36-7f15-9fa4-d63848443959" xlink:href="pstl-20260331.xsd#pstl_SellerFinancing2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_SellerFinancing2024Member_019cdd48-2b36-7f15-9fa4-d63848443959" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2030TermLoanMember_019cdd48-2b36-7e78-b0e3-9ad2313654fc" xlink:href="pstl-20260331.xsd#pstl_A2030TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_A2030TermLoanMember_019cdd48-2b36-7e78-b0e3-9ad2313654fc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2028TermLoanMember_019cdd48-2b36-78e3-9095-9c430045f11a" xlink:href="pstl-20260331.xsd#pstl_A2028TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_A2028TermLoanMember_019cdd48-2b36-78e3-9095-9c430045f11a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2022TermLoanMember_019cdd48-2b36-7b95-abdd-39a7560c7bc9" xlink:href="pstl-20260331.xsd#pstl_A2022TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_A2022TermLoanMember_019cdd48-2b36-7b95-abdd-39a7560c7bc9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2029RevolverMember_019cdd48-2b36-7bfd-8686-b44085074e44" xlink:href="pstl-20260331.xsd#pstl_A2029RevolverMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7ee1-8f7f-f2797cc64abf" xlink:to="loc_pstl_A2029RevolverMember_019cdd48-2b36-7bfd-8686-b44085074e44" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019cdd48-2b36-7585-8a98-a3f0da21e63d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019cdd48-2b36-7585-8a98-a3f0da21e63d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_019cdd48-2b36-7a36-9018-f1b80a41630e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_019cdd48-2b36-7a36-9018-f1b80a41630e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019cdd48-2b36-7846-8d21-8fc2416a4f30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019cdd48-2b36-7846-8d21-8fc2416a4f30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019cdd48-2b36-72ff-b245-55600079ac8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_LongTermDebt_019cdd48-2b36-72ff-b245-55600079ac8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019cdd48-2b36-755e-996a-64a0cb51895d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019cdd48-2b36-755e-996a-64a0cb51895d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cdd48-2b36-7fa2-aa23-24aa95deb445" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7dca-965b-0e35316929f6" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cdd48-2b36-7fa2-aa23-24aa95deb445" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/DebtExplanatorynotesDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#DebtExplanatorynotesDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/DebtExplanatorynotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-795b-8f55-71a41c3bc80f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-795b-8f55-71a41c3bc80f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-795b-8f55-71a41c3bc80f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-795b-8f55-71a41c3bc80f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-795b-8f55-71a41c3bc80f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-795b-8f55-71a41c3bc80f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2021TermLoanMember_019cdd48-2b36-7d7a-9fe2-288212a660d6" xlink:href="pstl-20260331.xsd#pstl_A2021TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_A2021TermLoanMember_019cdd48-2b36-7d7a-9fe2-288212a660d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2022TermLoanMember_019cdd48-2b36-774e-82ea-a9a198ec62a6" xlink:href="pstl-20260331.xsd#pstl_A2022TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_A2022TermLoanMember_019cdd48-2b36-774e-82ea-a9a198ec62a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_VisionBankMember_019cdd48-2b36-7afa-8c6a-406677dd01c0" xlink:href="pstl-20260331.xsd#pstl_VisionBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_VisionBankMember_019cdd48-2b36-7afa-8c6a-406677dd01c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7e01-9ece-a30c49177691" xlink:href="pstl-20260331.xsd#pstl_FirstOklahomaBankLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7e01-9ece-a30c49177691" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_VisionBankTwoThousandEighteenMember_019cdd48-2b36-7dfa-acaa-672b71ed284e" xlink:href="pstl-20260331.xsd#pstl_VisionBankTwoThousandEighteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_VisionBankTwoThousandEighteenMember_019cdd48-2b36-7dfa-acaa-672b71ed284e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SellerFinancing2024Member_019cdd48-2b36-7642-9474-3a3379ecc144" xlink:href="pstl-20260331.xsd#pstl_SellerFinancing2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_SellerFinancing2024Member_019cdd48-2b36-7642-9474-3a3379ecc144" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2030TermLoanMember_019cdd48-2b36-7b9f-99fa-98f20d11a3a4" xlink:href="pstl-20260331.xsd#pstl_A2030TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_A2030TermLoanMember_019cdd48-2b36-7b9f-99fa-98f20d11a3a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_TermLoanFacilityMember_019cdd48-2b36-7c41-abaa-70f0629db744" xlink:href="pstl-20260331.xsd#pstl_TermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_TermLoanFacilityMember_019cdd48-2b36-7c41-abaa-70f0629db744" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-79d0-9e57-d3297bfde1ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-79d0-9e57-d3297bfde1ad" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2028TermLoanMember_019cdd48-2b36-79f4-8689-1a9ae04dc0ce" xlink:href="pstl-20260331.xsd#pstl_A2028TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_A2028TermLoanMember_019cdd48-2b36-79f4-8689-1a9ae04dc0ce" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_A2029RevolverMember_019cdd48-2b36-7ea8-b13a-3bfbe34e5ad7" xlink:href="pstl-20260331.xsd#pstl_A2029RevolverMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-7bbf-a7c1-07b013f8694c" xlink:to="loc_pstl_A2029RevolverMember_019cdd48-2b36-7ea8-b13a-3bfbe34e5ad7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-7218-8169-e7e98dbf0f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-7218-8169-e7e98dbf0f9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7218-8169-e7e98dbf0f9b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-7218-8169-e7e98dbf0f9b" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7218-8169-e7e98dbf0f9b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7ca4-b2e4-ca6cef69a26f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b36-7218-8169-e7e98dbf0f9b" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7ca4-b2e4-ca6cef69a26f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-70ed-815d-c7720d924d37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7ca4-b2e4-ca6cef69a26f" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b36-70ed-815d-c7720d924d37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019cdd48-2b36-7656-93a9-baab2a1969eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cdd48-2b36-7ca4-b2e4-ca6cef69a26f" xlink:to="loc_us-gaap_UnsecuredDebtMember_019cdd48-2b36-7656-93a9-baab2a1969eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-74ca-ae15-a1b980131b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-74ca-ae15-a1b980131b0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-74ca-ae15-a1b980131b0f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-74ca-ae15-a1b980131b0f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-74ca-ae15-a1b980131b0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-707f-95eb-dc6bd3204233" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-74ca-ae15-a1b980131b0f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-707f-95eb-dc6bd3204233" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019cdd48-2b36-71e0-8fca-4e566bb66fb5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-707f-95eb-dc6bd3204233" xlink:to="loc_us-gaap_LineOfCreditMember_019cdd48-2b36-71e0-8fca-4e566bb66fb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7788-9651-eadeaf8dabe1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-707f-95eb-dc6bd3204233" xlink:to="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7788-9651-eadeaf8dabe1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019cdd48-2b36-7fc2-895a-61fb46df3f2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_us-gaap_VariableRateAxis_019cdd48-2b36-7fc2-895a-61fb46df3f2e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019cdd48-2b36-7fc2-895a-61fb46df3f2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019cdd48-2b36-7fc2-895a-61fb46df3f2e" xlink:to="loc_us-gaap_VariableRateDomain_019cdd48-2b36-7fc2-895a-61fb46df3f2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019cdd48-2b36-7fc2-895a-61fb46df3f2e" xlink:to="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019cdd48-2b36-755e-93bf-6eaa2496b474" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019cdd48-2b36-755e-93bf-6eaa2496b474" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019cdd48-2b36-7bb4-8903-bd9bb2fcadb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:to="loc_us-gaap_BaseRateMember_019cdd48-2b36-7bb4-8903-bd9bb2fcadb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UsTreasuryUstInterestRateMember_019cdd48-2b36-723e-ba35-b69938e3bc6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UsTreasuryUstInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:to="loc_us-gaap_UsTreasuryUstInterestRateMember_019cdd48-2b36-723e-ba35-b69938e3bc6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrimeRateMember_019cdd48-2b36-77b5-b071-77daecf2012e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrimeRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019cdd48-2b36-71d5-a90e-48e1ea69346f" xlink:to="loc_us-gaap_PrimeRateMember_019cdd48-2b36-77b5-b071-77daecf2012e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019cdd48-2b36-735c-91d8-aaea77342c09" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_srt_RangeAxis_019cdd48-2b36-735c-91d8-aaea77342c09" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-735c-91d8-aaea77342c09_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-735c-91d8-aaea77342c09" xlink:to="loc_srt_RangeMember_019cdd48-2b36-735c-91d8-aaea77342c09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-7c13-bd78-4fbf624d0e60" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-735c-91d8-aaea77342c09" xlink:to="loc_srt_RangeMember_019cdd48-2b36-7c13-bd78-4fbf624d0e60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019cdd48-2b36-740d-aa6f-b17299797fc2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cdd48-2b36-7c13-bd78-4fbf624d0e60" xlink:to="loc_srt_MinimumMember_019cdd48-2b36-740d-aa6f-b17299797fc2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019cdd48-2b36-7986-9aa5-eeb3f5d93ee6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cdd48-2b36-7c13-bd78-4fbf624d0e60" xlink:to="loc_srt_MaximumMember_019cdd48-2b36-7986-9aa5-eeb3f5d93ee6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditCommitmentFeeThresholdAxis_019cdd48-2b36-7519-80b8-b1c197ac4945" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditCommitmentFeeThresholdAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cdd48-2b36-74c2-9c8b-820fef045d3a" xlink:to="loc_pstl_LineOfCreditCommitmentFeeThresholdAxis_019cdd48-2b36-7519-80b8-b1c197ac4945" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7519-80b8-b1c197ac4945_default" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditCommitmentFeeThresholdDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pstl_LineOfCreditCommitmentFeeThresholdAxis_019cdd48-2b36-7519-80b8-b1c197ac4945" xlink:to="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7519-80b8-b1c197ac4945_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7f1b-9485-e469f0a75c25" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditCommitmentFeeThresholdDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pstl_LineOfCreditCommitmentFeeThresholdAxis_019cdd48-2b36-7519-80b8-b1c197ac4945" xlink:to="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7f1b-9485-e469f0a75c25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_CommitmentFeeThresholdOneMember_019cdd48-2b36-71c6-a79b-fff9ebb859f1" xlink:href="pstl-20260331.xsd#pstl_CommitmentFeeThresholdOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7f1b-9485-e469f0a75c25" xlink:to="loc_pstl_CommitmentFeeThresholdOneMember_019cdd48-2b36-71c6-a79b-fff9ebb859f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_CommitmentFeeThresholdTwoMember_019cdd48-2b36-7376-b444-edbcbbe3cacb" xlink:href="pstl-20260331.xsd#pstl_CommitmentFeeThresholdTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_LineOfCreditCommitmentFeeThresholdDomain_019cdd48-2b36-7f1b-9485-e469f0a75c25" xlink:to="loc_pstl_CommitmentFeeThresholdTwoMember_019cdd48-2b36-7376-b444-edbcbbe3cacb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019cdd48-2b36-7c69-b249-a38337521c81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019cdd48-2b36-7c69-b249-a38337521c81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019cdd48-2b36-7f6d-a8e4-d4a9eb48deac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019cdd48-2b36-7f6d-a8e4-d4a9eb48deac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019cdd48-2b36-744f-a56c-61618f63dffb" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019cdd48-2b36-744f-a56c-61618f63dffb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentBasisSpreadOnVariableRateIncreaseDecrease_019cdd48-2b36-701e-bd21-adbdd4b08faa" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentBasisSpreadOnVariableRateIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentBasisSpreadOnVariableRateIncreaseDecrease_019cdd48-2b36-701e-bd21-adbdd4b08faa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditFacilityNumberOfOptionsToExtend_019cdd48-2b36-76a4-8c57-75f05ec7ccda" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditFacilityNumberOfOptionsToExtend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_LineOfCreditFacilityNumberOfOptionsToExtend_019cdd48-2b36-76a4-8c57-75f05ec7ccda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditFacilityExtensionPeriod_019cdd48-2b36-7405-ba11-a389a71e1dd7" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditFacilityExtensionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_LineOfCreditFacilityExtensionPeriod_019cdd48-2b36-7405-ba11-a389a71e1dd7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019cdd48-2b36-7786-8717-3bfe33d54838" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019cdd48-2b36-7786-8717-3bfe33d54838" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentageThreshold_019cdd48-2b36-70b5-8b1f-ee42ac3219a3" xlink:href="pstl-20260331.xsd#pstl_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentageThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentageThreshold_019cdd48-2b36-70b5-8b1f-ee42ac3219a3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019cdd48-2b36-7b31-81a0-4985ef45a481" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019cdd48-2b36-7b31-81a0-4985ef45a481" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_019cdd48-2b36-7935-9265-4ee7f3246b10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_019cdd48-2b36-7935-9265-4ee7f3246b10" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentVariableRateAdjustment_019cdd48-2b36-7351-a420-81e083894d47" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentVariableRateAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentVariableRateAdjustment_019cdd48-2b36-7351-a420-81e083894d47" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentVariableRateFloor_019cdd48-2b36-7a71-b3da-3b071cb39e8c" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentVariableRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentVariableRateFloor_019cdd48-2b36-7a71-b3da-3b071cb39e8c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentNumberOfPropertiesCollateralizedUnderLoan_019cdd48-2b36-7fc3-8ec9-13bda7463a1f" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentNumberOfPropertiesCollateralizedUnderLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentNumberOfPropertiesCollateralizedUnderLoan_019cdd48-2b36-7fc3-8ec9-13bda7463a1f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentRemainingPercentageCollateralizedUnderLoan_019cdd48-2b36-77c4-b791-f1cda74b5d25" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentRemainingPercentageCollateralizedUnderLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentRemainingPercentageCollateralizedUnderLoan_019cdd48-2b36-77c4-b791-f1cda74b5d25" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cdd48-2b36-79ff-aef0-d9633b5a9c34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cdd48-2b36-79ff-aef0-d9633b5a9c34" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentInterestRateFixedRatePeriod_019cdd48-2b36-7f44-ad80-594b3317c7c1" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentInterestRateFixedRatePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentInterestRateFixedRatePeriod_019cdd48-2b36-7f44-ad80-594b3317c7c1" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_019cdd48-2b36-780e-927c-6106980262c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_019cdd48-2b36-780e-927c-6106980262c6" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentFixedInterestPeriod_019cdd48-2b36-79d3-a074-3c17255db36f" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentFixedInterestPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentFixedInterestPeriod_019cdd48-2b36-79d3-a074-3c17255db36f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentRemainingDiscountAmortizationPeriod_019cdd48-2b36-7cef-8c02-72b359351170" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentRemainingDiscountAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentRemainingDiscountAmortizationPeriod_019cdd48-2b36-7cef-8c02-72b359351170" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesAcquired_019cdd48-2b36-7e26-ba20-aabc8df96f32" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_NumberOfPropertiesAcquired_019cdd48-2b36-7e26-ba20-aabc8df96f32" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_WeightedAverageMaturityDateForSecuredBorrowingTerm_019cdd48-2b36-715e-9107-8e96b34f1787" xlink:href="pstl-20260331.xsd#pstl_WeightedAverageMaturityDateForSecuredBorrowingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_WeightedAverageMaturityDateForSecuredBorrowingTerm_019cdd48-2b36-715e-9107-8e96b34f1787" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019cdd48-2b36-7f38-a629-dc4c5d228cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019cdd48-2b36-7f38-a629-dc4c5d228cd5" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfUnsecuredDebt_019cdd48-2b36-79b5-a33f-d168d345d757" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfUnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfUnsecuredDebt_019cdd48-2b36-79b5-a33f-d168d345d757" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_019cdd48-2b36-7db5-9777-05ea213619f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_019cdd48-2b36-7db5-9777-05ea213619f4" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DebtInstrumentModificationFees_019cdd48-2b36-7400-bef6-7a225514fb57" xlink:href="pstl-20260331.xsd#pstl_DebtInstrumentModificationFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_pstl_DebtInstrumentModificationFees_019cdd48-2b36-7400-bef6-7a225514fb57" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCollateralAmount_019def5d-14f9-7f5b-9bae-eab156a186e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCollateralAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cdd48-2b36-7c54-99a1-621914beea8a" xlink:to="loc_us-gaap_DebtInstrumentCollateralAmount_019def5d-14f9-7f5b-9bae-eab156a186e0" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#DerivativesandHedgingActivitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019cdd48-2b36-784c-82e2-b35eecae7b08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_us-gaap_DerivativeTable_019cdd48-2b36-784c-82e2-b35eecae7b08" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019cdd48-2b36-784c-82e2-b35eecae7b08" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7fd2-aeb1-e8bfae514e3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7e6a-9974-3a9f82d6ab1f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7fd2-aeb1-e8bfae514e3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019cdd48-2b36-70a7-98e8-d45549635067" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7fd2-aeb1-e8bfae514e3f" xlink:to="loc_us-gaap_InterestRateSwapMember_019cdd48-2b36-70a7-98e8-d45549635067" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNumberOfInstrumentsHeld_019cdd48-2b36-7c96-b410-e6134655b0ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetNumberOfInstrumentsHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_us-gaap_DerivativeAssetNumberOfInstrumentsHeld_019cdd48-2b36-7c96-b410-e6134655b0ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019cdd48-2b36-7af7-b981-69cf83a75a85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019cdd48-2b36-7af7-b981-69cf83a75a85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019cdd48-2b36-7219-b506-34eca4d2de2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019cdd48-2b36-7219-b506-34eca4d2de2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019cdd48-2b36-7d3d-a501-5f8b6bdc82e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019cdd48-2b36-7d3d-a501-5f8b6bdc82e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_DerivativeLiabilityPotentialSettlementPayment_019cdd48-2b36-7d63-919e-e18f1380f84a" xlink:href="pstl-20260331.xsd#pstl_DerivativeLiabilityPotentialSettlementPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7daf-aaaf-084114971358" xlink:to="loc_pstl_DerivativeLiabilityPotentialSettlementPayment_019cdd48-2b36-7d63-919e-e18f1380f84a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesComponentsofinterestrateswapDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#DerivativesandHedgingActivitiesComponentsofinterestrateswapDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesComponentsofinterestrateswapDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7262-8fd7-e6de0976f601" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019cdd48-2b36-7a95-b33c-6515fa6e7bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7262-8fd7-e6de0976f601" xlink:to="loc_us-gaap_DerivativeTable_019cdd48-2b36-7a95-b33c-6515fa6e7bc1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-743e-97c1-3ecded2fe3ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019cdd48-2b36-7a95-b33c-6515fa6e7bc1" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-743e-97c1-3ecded2fe3ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-743e-97c1-3ecded2fe3ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-743e-97c1-3ecded2fe3ca" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-743e-97c1-3ecded2fe3ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-743e-97c1-3ecded2fe3ca" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfJanuary2027Member_019cdd48-2b36-7081-bce5-b2e0653d9a3a" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveMay2022MaturityOfJanuary2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfJanuary2027Member_019cdd48-2b36-7081-bce5-b2e0653d9a3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028Member_019cdd48-2b36-7bd9-89a1-6384280e8bb9" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028Member_019cdd48-2b36-7bd9-89a1-6384280e8bb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028TwoMember_019cdd48-2b36-75fc-b8df-e35adc4f21eb" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028TwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveMay2022MaturityOfFebruary2028TwoMember_019cdd48-2b36-75fc-b8df-e35adc4f21eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveJuly2022MaturityOfFebruary2028Member_019cdd48-2b36-72eb-a733-6319a7a5ac1b" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveJuly2022MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveJuly2022MaturityOfFebruary2028Member_019cdd48-2b36-72eb-a733-6319a7a5ac1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveDecember2022MaturityOfFebruary2028Member_019cdd48-2b36-7c94-ae5e-e491c773cf1e" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveDecember2022MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveDecember2022MaturityOfFebruary2028Member_019cdd48-2b36-7c94-ae5e-e491c773cf1e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveJuly2023MaturityOfJanuary2027Member_019cdd48-2b36-792a-a244-9ae7f8cbf90f" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveJuly2023MaturityOfJanuary2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveJuly2023MaturityOfJanuary2027Member_019cdd48-2b36-792a-a244-9ae7f8cbf90f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveSeptember2023MaturityOfFebruary2028Member_019cdd48-2b36-716a-b5c0-131e6ce691e2" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveSeptember2023MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveSeptember2023MaturityOfFebruary2028Member_019cdd48-2b36-716a-b5c0-131e6ce691e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveOctober2024MaturityOfFebruary2028Member_019cdd48-2b36-7147-8653-dc7dfd5087bd" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveOctober2024MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveOctober2024MaturityOfFebruary2028Member_019cdd48-2b36-7147-8653-dc7dfd5087bd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveNovember2024MaturityOfFebruary2028Member_019cdd48-2b36-778c-8d59-e93dd6b90b5a" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveNovember2024MaturityOfFebruary2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveNovember2024MaturityOfFebruary2028Member_019cdd48-2b36-778c-8d59-e93dd6b90b5a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary2030Member_019cdd48-2b36-759f-abc5-e30cb5f9b622" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary2030Member_019cdd48-2b36-759f-abc5-e30cb5f9b622" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary203030MMember_019cdd48-2b36-71f5-9437-37070f250f10" xlink:href="pstl-20260331.xsd#pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary203030MMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7115-af5b-ddfab1884ca1" xlink:to="loc_pstl_InterestRateSwapEffectiveSeptember2025MaturityOfJanuary203030MMember_019cdd48-2b36-71f5-9437-37070f250f10" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019cdd48-2b36-7d14-8e5d-49138a29e7cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7262-8fd7-e6de0976f601" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019cdd48-2b36-7d14-8e5d-49138a29e7cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_019cdd48-2b36-7d6a-94f0-fd05a4286b10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-7262-8fd7-e6de0976f601" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_019cdd48-2b36-7d6a-94f0-fd05a4286b10" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesInterestrateswapinOCIandincomestatementDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#DerivativesandHedgingActivitiesInterestrateswapinOCIandincomestatementDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/DerivativesandHedgingActivitiesInterestrateswapinOCIandincomestatementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-73a5-ba51-e229e69b0cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019cdd48-2b36-7c69-8f02-79cd5fb3fd4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-73a5-ba51-e229e69b0cb5" xlink:to="loc_us-gaap_DerivativeTable_019cdd48-2b36-7c69-8f02-79cd5fb3fd4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7b48-a4e3-eaee3c7fc209" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019cdd48-2b36-7c69-8f02-79cd5fb3fd4d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7b48-a4e3-eaee3c7fc209" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7b48-a4e3-eaee3c7fc209_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7b48-a4e3-eaee3c7fc209" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7b48-a4e3-eaee3c7fc209_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7eff-8fc9-9a03afceef75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019cdd48-2b36-7b48-a4e3-eaee3c7fc209" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7eff-8fc9-9a03afceef75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019cdd48-2b36-70da-98a2-448bbca6d64f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019cdd48-2b36-7eff-8fc9-9a03afceef75" xlink:to="loc_us-gaap_InterestRateSwapMember_019cdd48-2b36-70da-98a2-448bbca6d64f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019cdd48-2b36-7304-bc50-37f3aa29e8e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-73a5-ba51-e229e69b0cb5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019cdd48-2b36-7304-bc50-37f3aa29e8e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019cdd48-2b36-7fab-973b-18dc60771428" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019cdd48-2b36-73a5-ba51-e229e69b0cb5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019cdd48-2b36-7fab-973b-18dc60771428" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/LeasesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeasedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019cdd48-2b36-7abb-bbb6-5b9f7a3dca3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019cdd48-2b36-7abb-bbb6-5b9f7a3dca3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019cdd48-2b36-7441-951b-86b8dd0d0085" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019cdd48-2b36-7abb-bbb6-5b9f7a3dca3d" xlink:to="loc_srt_RangeAxis_019cdd48-2b36-7441-951b-86b8dd0d0085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-7441-951b-86b8dd0d0085_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-7441-951b-86b8dd0d0085" xlink:to="loc_srt_RangeMember_019cdd48-2b36-7441-951b-86b8dd0d0085_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-76eb-8ad0-92143e4a7584" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-7441-951b-86b8dd0d0085" xlink:to="loc_srt_RangeMember_019cdd48-2b36-76eb-8ad0-92143e4a7584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019cdd48-2b36-743b-b3df-2d6154d5577f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cdd48-2b36-76eb-8ad0-92143e4a7584" xlink:to="loc_srt_MinimumMember_019cdd48-2b36-743b-b3df-2d6154d5577f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019cdd48-2b36-7e8c-85db-2466bce351c3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cdd48-2b36-76eb-8ad0-92143e4a7584" xlink:to="loc_srt_MaximumMember_019cdd48-2b36-7e8c-85db-2466bce351c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorDirectFinancingLeaseNumber_019cdd48-2b36-7de6-a924-2b84c0ee8c8c" xlink:href="pstl-20260331.xsd#pstl_LessorDirectFinancingLeaseNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorDirectFinancingLeaseNumber_019cdd48-2b36-7de6-a924-2b84c0ee8c8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumber_019cdd48-2b36-76a2-9718-14d073182624" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumber_019cdd48-2b36-76a2-9718-14d073182624" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceGreaterThanValueOfUnderlyingAsset_019cdd48-2b36-713b-a3a7-5f62848a9dfb" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceGreaterThanValueOfUnderlyingAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceGreaterThanValueOfUnderlyingAsset_019cdd48-2b36-713b-a3a7-5f62848a9dfb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetAggregateCarryingValue_019cdd48-2b36-7214-aac6-961c8cb9a3c4" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetAggregateCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetAggregateCarryingValue_019cdd48-2b36-7214-aac6-961c8cb9a3c4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetPurchasePriceGreaterThanValueOfUnderlyingAssetsAggregatePurchasePrice_019cdd48-2b36-7f9c-ace2-6226760f8017" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetPurchasePriceGreaterThanValueOfUnderlyingAssetsAggregatePurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetPurchasePriceGreaterThanValueOfUnderlyingAssetsAggregatePurchasePrice_019cdd48-2b36-7f9c-ace2-6226760f8017" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceLessThanOrEqualToUnderlyingAsset_019cdd48-2b36-7ce0-9ece-83391047f3fa" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceLessThanOrEqualToUnderlyingAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetNumberPurchasePriceLessThanOrEqualToUnderlyingAsset_019cdd48-2b36-7ce0-9ece-83391047f3fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetsNumberPurchasePriceLessThanOrEqualToUnderlyingAssetConsideration_019cdd48-2b36-7d74-8e25-c092b5905d61" xlink:href="pstl-20260331.xsd#pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetsNumberPurchasePriceLessThanOrEqualToUnderlyingAssetConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_pstl_LessorOperatingLeaseLesseeOptionToPurchaseUnderlyingAssetsNumberPurchasePriceLessThanOrEqualToUnderlyingAssetConsideration_019cdd48-2b36-7d74-8e25-c092b5905d61" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DirectFinancingLeaseRevenue_019cdd48-2b36-7f65-9d17-9b770cba407d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DirectFinancingLeaseRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_DirectFinancingLeaseRevenue_019cdd48-2b36-7f65-9d17-9b770cba407d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019cdd48-2b36-779f-92a7-44dc24d61b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019cdd48-2b36-779f-92a7-44dc24d61b2e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_019cdd48-2b36-7baa-bac7-e0525aa99619" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_019cdd48-2b36-7baa-bac7-e0525aa99619" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_019cdd48-2b36-7f7a-8f72-e6cdb2a19145" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_019cdd48-2b36-7f7a-8f72-e6cdb2a19145" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_019cdd48-2b36-7f86-ba46-e50d66723245" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019cdd48-2b36-7c99-b4f1-40dfc494e9aa" xlink:to="loc_us-gaap_OperatingLeaseExpense_019cdd48-2b36-7f86-ba46-e50d66723245" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_019cdd48-2b36-724c-ab12-5eca3aeead92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxContingencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_019cdd48-2b36-7365-be5a-7fd05c4b8a7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxContingencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_019cdd48-2b36-724c-ab12-5eca3aeead92" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_019cdd48-2b36-7365-be5a-7fd05c4b8a7e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7e8f-bca9-b40e60b09bec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_019cdd48-2b36-7365-be5a-7fd05c4b8a7e" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7e8f-bca9-b40e60b09bec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7e8f-bca9-b40e60b09bec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7e8f-bca9-b40e60b09bec" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7e8f-bca9-b40e60b09bec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7002-8b91-658906c05383" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7e8f-bca9-b40e60b09bec" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7002-8b91-658906c05383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2b36-708a-ac74-7bc3329dd108" xlink:href="pstl-20260331.xsd#pstl_RealEstateAssetCounselingLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7002-8b91-658906c05383" xlink:to="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2b36-708a-ac74-7bc3329dd108" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019cdd48-2b36-741a-8b88-32b7f2f2f388" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_019cdd48-2b36-7365-be5a-7fd05c4b8a7e" xlink:to="loc_dei_LegalEntityAxis_019cdd48-2b36-741a-8b88-32b7f2f2f388" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2b36-741a-8b88-32b7f2f2f388_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2b36-741a-8b88-32b7f2f2f388" xlink:to="loc_dei_EntityDomain_019cdd48-2b36-741a-8b88-32b7f2f2f388_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2b36-7d1f-b312-1ca0946ad57f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2b36-741a-8b88-32b7f2f2f388" xlink:to="loc_dei_EntityDomain_019cdd48-2b36-7d1f-b312-1ca0946ad57f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2b36-7f91-b5e6-bfd0dd93c371" xlink:href="pstl-20260331.xsd#pstl_RealEstateAssetCounselingLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019cdd48-2b36-7d1f-b312-1ca0946ad57f" xlink:to="loc_pstl_RealEstateAssetCounselingLLCMember_019cdd48-2b36-7f91-b5e6-bfd0dd93c371" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019cdd48-2b36-73c6-89ed-023526fbadbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_019cdd48-2b36-724c-ab12-5eca3aeead92" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019cdd48-2b36-73c6-89ed-023526fbadbd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#RelatedPartyTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:href="pstl-20260331.xsd#pstl_RelatedPartyTransactionsDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:href="pstl-20260331.xsd#pstl_RelatedPartyTransactionsDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019cdd48-2b36-7a96-b5cc-dc128547cafd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019cdd48-2b36-7a96-b5cc-dc128547cafd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7a96-b5cc-dc128547cafd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019cdd48-2b36-7a96-b5cc-dc128547cafd" xlink:to="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7a96-b5cc-dc128547cafd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7964-83d5-293d4d543c5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019cdd48-2b36-7a96-b5cc-dc128547cafd" xlink:to="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7964-83d5-293d4d543c5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_019cdd48-2b36-7ad9-bee8-2c2acff7207e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7964-83d5-293d4d543c5d" xlink:to="loc_srt_AffiliatedEntityMember_019cdd48-2b36-7ad9-bee8-2c2acff7207e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b36-7a6a-a110-9b28c05ef6c5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7964-83d5-293d4d543c5d" xlink:to="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b36-7a6a-a110-9b28c05ef6c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dec06-5c69-77dd-b2a3-2d54427e2e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019cdd48-2b36-7964-83d5-293d4d543c5d" xlink:to="loc_us-gaap_RelatedPartyMember_019dec06-5c69-77dd-b2a3-2d54427e2e6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019cdd48-2b36-7320-af90-615c295157ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019cdd48-2b36-7320-af90-615c295157ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7320-af90-615c295157ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019cdd48-2b36-7320-af90-615c295157ad" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7320-af90-615c295157ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7f30-990d-3461945d9777" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019cdd48-2b36-7320-af90-615c295157ad" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7f30-990d-3461945d9777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_InitialManagementFeeRatePerAnnumOfPropertysGrossRevenueMember_019cdd48-2b36-758f-b32e-f7ab14c02320" xlink:href="pstl-20260331.xsd#pstl_InitialManagementFeeRatePerAnnumOfPropertysGrossRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7f30-990d-3461945d9777" xlink:to="loc_pstl_InitialManagementFeeRatePerAnnumOfPropertysGrossRevenueMember_019cdd48-2b36-758f-b32e-f7ab14c02320" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_IncreaseInManagementFeeMember_019cdd48-2b36-7f50-9be0-aeb648ae3206" xlink:href="pstl-20260331.xsd#pstl_IncreaseInManagementFeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019cdd48-2b36-7f30-990d-3461945d9777" xlink:to="loc_pstl_IncreaseInManagementFeeMember_019cdd48-2b36-7f50-9be0-aeb648ae3206" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019cdd48-2b36-755f-9707-77c7ffa03324" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_dei_LegalEntityAxis_019cdd48-2b36-755f-9707-77c7ffa03324" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2b36-755f-9707-77c7ffa03324_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2b36-755f-9707-77c7ffa03324" xlink:to="loc_dei_EntityDomain_019cdd48-2b36-755f-9707-77c7ffa03324_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019cdd48-2b36-7efc-8079-e865f45076b8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019cdd48-2b36-755f-9707-77c7ffa03324" xlink:to="loc_dei_EntityDomain_019cdd48-2b36-7efc-8079-e865f45076b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PostalRealtyManagementMember_019cdd48-2b36-7c09-9052-a498c638d9b9" xlink:href="pstl-20260331.xsd#pstl_PostalRealtyManagementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019cdd48-2b36-7efc-8079-e865f45076b8" xlink:to="loc_pstl_PostalRealtyManagementMember_019cdd48-2b36-7c09-9052-a498c638d9b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-733d-9879-234e79d7e140" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-733d-9879-234e79d7e140" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-733d-9879-234e79d7e140_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-733d-9879-234e79d7e140" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-733d-9879-234e79d7e140_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-70a0-affd-5d96eca46731" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cdd48-2b36-733d-9879-234e79d7e140" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-70a0-affd-5d96eca46731" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7734-aa31-7534952bea88" xlink:href="pstl-20260331.xsd#pstl_FirstOklahomaBankLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cdd48-2b36-70a0-affd-5d96eca46731" xlink:to="loc_pstl_FirstOklahomaBankLoanMember_019cdd48-2b36-7734-aa31-7534952bea88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7830-b973-060c65a30c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7830-b973-060c65a30c0c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7830-b973-060c65a30c0c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7830-b973-060c65a30c0c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7830-b973-060c65a30c0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7126-8b0e-a85d1fef942a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b36-7830-b973-060c65a30c0c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7126-8b0e-a85d1fef942a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7451-9087-09b6457bdab2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b36-7126-8b0e-a85d1fef942a" xlink:to="loc_us-gaap_LoansPayableMember_019cdd48-2b36-7451-9087-09b6457bdab2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019cdd48-2b36-745c-8629-9e47fd40f87c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_srt_RangeAxis_019cdd48-2b36-745c-8629-9e47fd40f87c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-745c-8629-9e47fd40f87c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-745c-8629-9e47fd40f87c" xlink:to="loc_srt_RangeMember_019cdd48-2b36-745c-8629-9e47fd40f87c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cdd48-2b36-771a-a8c2-a7b857fffe3d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019cdd48-2b36-745c-8629-9e47fd40f87c" xlink:to="loc_srt_RangeMember_019cdd48-2b36-771a-a8c2-a7b857fffe3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019cdd48-2b36-70bc-9a7a-83894dcec011" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cdd48-2b36-771a-a8c2-a7b857fffe3d" xlink:to="loc_srt_MaximumMember_019cdd48-2b36-70bc-9a7a-83894dcec011" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019dda23-a78f-7653-a98c-2bd84e364da1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsTable_019cdd48-2b36-73b3-a6af-aec962c92bb7" xlink:to="loc_srt_CounterpartyNameAxis_019dda23-a78f-7653-a98c-2bd84e364da1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dda23-a78f-7653-a98c-2bd84e364da1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019dda23-a78f-7653-a98c-2bd84e364da1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dda23-a78f-7653-a98c-2bd84e364da1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dda23-a78f-7adb-88a8-5ec83d4cf175" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019dda23-a78f-7653-a98c-2bd84e364da1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dda23-a78f-7adb-88a8-5ec83d4cf175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AndrewSpodekChiefExecutiveOfficerMember_019dda23-a78f-7f1e-bbf9-7193d23b2e03" xlink:href="pstl-20260331.xsd#pstl_AndrewSpodekChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dda23-a78f-7adb-88a8-5ec83d4cf175" xlink:to="loc_pstl_AndrewSpodekChiefExecutiveOfficerMember_019dda23-a78f-7f1e-bbf9-7193d23b2e03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfRealEstateProperties_019cdd48-2b36-785f-bf67-c412126f5ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfRealEstateProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_NumberOfRealEstateProperties_019cdd48-2b36-785f-bf67-c412126f5ad4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyManagementFeePercentFee_019cdd48-2b36-7718-a01c-ba1de082f8b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyManagementFeePercentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_PropertyManagementFeePercentFee_019cdd48-2b36-7718-a01c-ba1de082f8b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ContractTerm_019cdd48-2b36-7b01-bb06-fba044555e4f" xlink:href="pstl-20260331.xsd#pstl_ContractTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_ContractTerm_019cdd48-2b36-7b01-bb06-fba044555e4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AdvanceNoticeOfNonRenewalPeriod_019cdd48-2b36-70d4-9345-5742b37946e5" xlink:href="pstl-20260331.xsd#pstl_AdvanceNoticeOfNonRenewalPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_AdvanceNoticeOfNonRenewalPeriod_019cdd48-2b36-70d4-9345-5742b37946e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ContractTerminationNoticePeriod_019cdd48-2b36-7524-9c76-2c76afbfc77a" xlink:href="pstl-20260331.xsd#pstl_ContractTerminationNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_ContractTerminationNoticePeriod_019cdd48-2b36-7524-9c76-2c76afbfc77a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PropertyManagementFee_019cdd48-2b36-7afe-8d3e-db0d32294974" xlink:href="pstl-20260331.xsd#pstl_PropertyManagementFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_PropertyManagementFee_019cdd48-2b36-7afe-8d3e-db0d32294974" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ManagementFeeIncome_019cdd48-2b36-7836-bcef-b7382004edfc" xlink:href="pstl-20260331.xsd#pstl_ManagementFeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_ManagementFeeIncome_019cdd48-2b36-7836-bcef-b7382004edfc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ManagementFeeReceivable_019cdd48-2b36-7c55-9aa4-d80a78fbe74a" xlink:href="pstl-20260331.xsd#pstl_ManagementFeeReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_ManagementFeeReceivable_019cdd48-2b36-7c55-9aa4-d80a78fbe74a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRent_019cdd48-2b36-74f8-b4d7-8577db89140c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_PaymentsForRent_019cdd48-2b36-74f8-b4d7-8577db89140c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_019cdd48-2b36-74db-81c1-8b16b90bf00b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_OperatingLeaseExpense_019cdd48-2b36-74db-81c1-8b16b90bf00b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019cdd48-2b36-7669-8e16-590e2d17af26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019cdd48-2b36-7669-8e16-590e2d17af26" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019cdd48-2b36-7896-84a4-4a75d8f84921" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019cdd48-2b36-7896-84a4-4a75d8f84921" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPostalPropertiesAcquired_019cdd48-2b36-7434-8cf8-70116cefd9c1" xlink:href="pstl-20260331.xsd#pstl_NumberOfPostalPropertiesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_NumberOfPostalPropertiesAcquired_019cdd48-2b36-7434-8cf8-70116cefd9c1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019cdd48-2b36-7a3c-91c3-71b11ff7ba68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019cdd48-2b36-7a3c-91c3-71b11ff7ba68" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesWithRightOfFirstOffer_019cdd48-2b36-7c6a-9751-3421cf8d169d" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesWithRightOfFirstOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_NumberOfPropertiesWithRightOfFirstOffer_019cdd48-2b36-7c6a-9751-3421cf8d169d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPropertiesAcquired_019cdd48-2b36-7894-abe1-b13985557393" xlink:href="pstl-20260331.xsd#pstl_NumberOfPropertiesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_pstl_NumberOfPropertiesAcquired_019cdd48-2b36-7894-abe1-b13985557393" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019cdd48-2b36-783b-b45c-1c6bd2f033f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_LongTermDebt_019cdd48-2b36-783b-b45c-1c6bd2f033f8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_019dec06-d2b3-789e-91e2-6d1291e01fef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireRealEstateHeldForInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_RelatedPartyTransactionsDetailsLineItems_019cdd48-2b36-7518-b636-6640a87c31ae" xlink:to="loc_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_019dec06-d2b3-789e-91e2-6d1291e01fef" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/EarningsPerShareScheduleofreconciliationofincomelossfromoperationsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#EarningsPerShareScheduleofreconciliationofincomelossfromoperationsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/EarningsPerShareScheduleofreconciliationofincomelossfromoperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019df432-9c2e-7c89-83d2-8837836d7715" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019df432-9c2e-77f6-aa38-7286d2b64edd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019df432-9c2e-7c89-83d2-8837836d7715" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019df432-9c2e-77f6-aa38-7286d2b64edd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019df432-9c2e-7fe7-af06-5f31b1805d70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019df432-9c2e-77f6-aa38-7286d2b64edd" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019df432-9c2e-7fe7-af06-5f31b1805d70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7fe7-af06-5f31b1805d70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019df432-9c2e-7fe7-af06-5f31b1805d70" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7fe7-af06-5f31b1805d70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7795-9f9a-a6056431ecea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019df432-9c2e-7fe7-af06-5f31b1805d70" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7795-9f9a-a6056431ecea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019df432-d94e-7e6a-9f15-8209f63aad4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7795-9f9a-a6056431ecea" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019df432-d94e-7e6a-9f15-8209f63aad4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityContractMember_019df434-484f-7be8-ab78-2063a1f2af29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019df432-9c2e-7795-9f9a-a6056431ecea" xlink:to="loc_us-gaap_EquityContractMember_019df434-484f-7be8-ab78-2063a1f2af29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019df432-9c2e-73e5-b637-96b7d9255f82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019df432-9c2e-7c89-83d2-8837836d7715" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019df432-9c2e-73e5-b637-96b7d9255f82" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityATMprogramDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityATMprogramDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityATMprogramDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7731-8b6e-f8f8426ce719" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-71aa-a3a3-d55ea5ddabef" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7731-8b6e-f8f8426ce719" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-71aa-a3a3-d55ea5ddabef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-793e-8a5c-3d19170a8b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-71aa-a3a3-d55ea5ddabef" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-793e-8a5c-3d19170a8b7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-793e-8a5c-3d19170a8b7d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-793e-8a5c-3d19170a8b7d" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-793e-8a5c-3d19170a8b7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75b0-a8c6-bddec3e50095" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-793e-8a5c-3d19170a8b7d" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75b0-a8c6-bddec3e50095" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2b36-7035-babf-0cb0c1525e37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75b0-a8c6-bddec3e50095" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2b36-7035-babf-0cb0c1525e37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7ef7-9a01-98e7c2d254ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-71aa-a3a3-d55ea5ddabef" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7ef7-9a01-98e7c2d254ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7ef7-9a01-98e7c2d254ef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7ef7-9a01-98e7c2d254ef" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7ef7-9a01-98e7c2d254ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7bc0-8846-abdd2a48c6a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-7ef7-9a01-98e7c2d254ef" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7bc0-8846-abdd2a48c6a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AtTheMarketOfferingProgramMember_019cdd48-2b36-7fc2-9668-8bf25132c41c" xlink:href="pstl-20260331.xsd#pstl_AtTheMarketOfferingProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-7bc0-8846-abdd2a48c6a0" xlink:to="loc_pstl_AtTheMarketOfferingProgramMember_019cdd48-2b36-7fc2-9668-8bf25132c41c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SaleOfStockConsiderationAuthorized_019cdd48-2b36-7eca-b98a-7c3d2f0863a7" xlink:href="pstl-20260331.xsd#pstl_SaleOfStockConsiderationAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7731-8b6e-f8f8426ce719" xlink:to="loc_pstl_SaleOfStockConsiderationAuthorized_019cdd48-2b36-7eca-b98a-7c3d2f0863a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019cdd48-2b36-7527-9088-9fc16854c1f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7731-8b6e-f8f8426ce719" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019cdd48-2b36-7527-9088-9fc16854c1f9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityActivityundertheATMProgramwithForwardSalesAgreementsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityActivityundertheATMProgramwithForwardSalesAgreementsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityActivityundertheATMProgramwithForwardSalesAgreementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019dda38-c986-753f-8ae5-c62bf73e51d3" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019dda38-c986-753f-8ae5-c62bf73e51d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019dda38-c986-7b29-9165-e1dd73242255" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019dda38-c986-753f-8ae5-c62bf73e51d3" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019dda38-c986-7b29-9165-e1dd73242255" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dda38-c986-7b29-9165-e1dd73242255_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dda38-c986-7b29-9165-e1dd73242255" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dda38-c986-7b29-9165-e1dd73242255_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dda38-c986-7e2c-86dc-056eeadc2475" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dda38-c986-7b29-9165-e1dd73242255" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dda38-c986-7e2c-86dc-056eeadc2475" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AtTheMarketProgramWithForwardSalesAgreementsMember_019dda38-c986-77d7-9bd7-12aded37efa0" xlink:href="pstl-20260331.xsd#pstl_AtTheMarketProgramWithForwardSalesAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dda38-c986-7e2c-86dc-056eeadc2475" xlink:to="loc_pstl_AtTheMarketProgramWithForwardSalesAgreementsMember_019dda38-c986-77d7-9bd7-12aded37efa0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SaleOfStockNumberOfSharesSoldInTransaction_019dda3b-a3aa-7efb-869b-75c7a6bcb4a8" xlink:href="pstl-20260331.xsd#pstl_SaleOfStockNumberOfSharesSoldInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:to="loc_pstl_SaleOfStockNumberOfSharesSoldInTransaction_019dda3b-a3aa-7efb-869b-75c7a6bcb4a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019dda38-c986-702b-ac65-123314f55e35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019dda38-c986-702b-ac65-123314f55e35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dda38-c986-76ae-9e7a-d685e7c2084d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dda38-c986-76ae-9e7a-d685e7c2084d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SaleOfStockEstimatedRemainingGrossProceeds_019dda3c-adc3-7c6e-ab01-57d9ee7595cb" xlink:href="pstl-20260331.xsd#pstl_SaleOfStockEstimatedRemainingGrossProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019dda38-c986-7f0a-b41e-9f94740fc50d" xlink:to="loc_pstl_SaleOfStockEstimatedRemainingGrossProceeds_019dda3c-adc3-7c6e-ab01-57d9ee7595cb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityActivityundertheATMProgramDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityActivityundertheATMProgramDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityActivityundertheATMProgramDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7496-b8bd-94aeb113b7d4" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7496-b8bd-94aeb113b7d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-78d4-963d-7f8b114540b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7496-b8bd-94aeb113b7d4" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-78d4-963d-7f8b114540b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-78d4-963d-7f8b114540b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-78d4-963d-7f8b114540b0" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-78d4-963d-7f8b114540b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-70a5-9db5-46657e52a29e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019cdd48-2b36-78d4-963d-7f8b114540b0" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-70a5-9db5-46657e52a29e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AtTheMarketOfferingProgramMember_019cdd48-2b36-7ca4-85f7-4634efe5e266" xlink:href="pstl-20260331.xsd#pstl_AtTheMarketOfferingProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019cdd48-2b36-70a5-9db5-46657e52a29e" xlink:to="loc_pstl_AtTheMarketOfferingProgramMember_019cdd48-2b36-7ca4-85f7-4634efe5e266" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019cdd48-2b36-7999-8888-a65b7c391967" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019cdd48-2b36-7999-8888-a65b7c391967" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019cdd48-2b36-7e9f-8966-bafbb216084b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019cdd48-2b36-7e9f-8966-bafbb216084b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_019cdd48-2b36-7f37-8cbc-c15c1c76f33f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_019cdd48-2b36-7f37-8cbc-c15c1c76f33f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019cdd48-2b36-74a8-a363-b23e5a058c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019cdd48-2b36-74a8-a363-b23e5a058c3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SaleOfStockAveragePricePerShare_019cdd48-2b36-738d-9a4f-48793baab815" xlink:href="pstl-20260331.xsd#pstl_SaleOfStockAveragePricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_pstl_SaleOfStockAveragePricePerShare_019cdd48-2b36-738d-9a4f-48793baab815" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_SaleOfStockOtherCostsIncurred_019df407-69af-7cbf-99fc-b0599c83420e" xlink:href="pstl-20260331.xsd#pstl_SaleOfStockOtherCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-705c-9009-44be0a74f7b9" xlink:to="loc_pstl_SaleOfStockOtherCostsIncurred_019df407-69af-7cbf-99fc-b0599c83420e" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityDividendsanddistributionsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityDividendsanddistributionsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityDividendsanddistributionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7649-9e11-4597a1077d04" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7637-b06d-41cc05ec43d0" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7649-9e11-4597a1077d04" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7637-b06d-41cc05ec43d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7a23-89dd-1bd5e60ffee2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-7637-b06d-41cc05ec43d0" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7a23-89dd-1bd5e60ffee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7a23-89dd-1bd5e60ffee2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7a23-89dd-1bd5e60ffee2" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7a23-89dd-1bd5e60ffee2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7757-9c5e-0187da01b58d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7a23-89dd-1bd5e60ffee2" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7757-9c5e-0187da01b58d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2b36-7f37-8227-0df5624eedf2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7757-9c5e-0187da01b58d" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2b36-7f37-8227-0df5624eedf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPaidinkind_019cdd48-2b36-7e7c-a674-32a5a58ad210" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPaidinkind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7649-9e11-4597a1077d04" xlink:to="loc_us-gaap_DividendsPaidinkind_019cdd48-2b36-7e7c-a674-32a5a58ad210" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareCashPaid_019cdd48-2b36-7315-b8bd-a3923471bb67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareCashPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7649-9e11-4597a1077d04" xlink:to="loc_us-gaap_CommonStockDividendsPerShareCashPaid_019cdd48-2b36-7315-b8bd-a3923471bb67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019cdd48-2b36-7215-80fa-a4daf0b3e771" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7649-9e11-4597a1077d04" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019cdd48-2b36-7215-80fa-a4daf0b3e771" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityNoncontrollinginterestsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityNoncontrollinginterestsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityNoncontrollinginterestsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019cdd48-2b36-722b-8bed-794902a34da7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_srt_TitleOfIndividualAxis_019cdd48-2b36-722b-8bed-794902a34da7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-722b-8bed-794902a34da7_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b36-722b-8bed-794902a34da7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-722b-8bed-794902a34da7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-79a7-9e4b-56fe3ec8d8ef" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b36-722b-8bed-794902a34da7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-79a7-9e4b-56fe3ec8d8ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b36-76a6-bf90-84de548346c8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-79a7-9e4b-56fe3ec8d8ef" xlink:to="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b36-76a6-bf90-84de548346c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PresidentMember_019cdd48-2b36-7171-8057-0f41c0c35440" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_PresidentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-79a7-9e4b-56fe3ec8d8ef" xlink:to="loc_srt_PresidentMember_019cdd48-2b36-7171-8057-0f41c0c35440" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeeMember_019cdd48-2b36-7779-8732-600c7ee4b83a" xlink:href="pstl-20260331.xsd#pstl_EmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b36-79a7-9e4b-56fe3ec8d8ef" xlink:to="loc_pstl_EmployeeMember_019cdd48-2b36-7779-8732-600c7ee4b83a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019cdd48-2b36-7b4e-b295-e916c178b09c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_us-gaap_PlanNameAxis_019cdd48-2b36-7b4e-b295-e916c178b09c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b36-7b4e-b295-e916c178b09c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b36-7b4e-b295-e916c178b09c" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b36-7b4e-b295-e916c178b09c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b36-7aa0-8b45-ac25685726f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b36-7b4e-b295-e916c178b09c" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b36-7aa0-8b45-ac25685726f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LongTermIncentivePlanMember_019cdd48-2b36-7ab9-836c-eacdeaa16f26" xlink:href="pstl-20260331.xsd#pstl_LongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019cdd48-2b36-7aa0-8b45-ac25685726f5" xlink:to="loc_pstl_LongTermIncentivePlanMember_019cdd48-2b36-7ab9-836c-eacdeaa16f26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b36-7816-afa9-74c89a72d584" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b36-7816-afa9-74c89a72d584" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2b36-7816-afa9-74c89a72d584_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b36-7816-afa9-74c89a72d584" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2b36-7816-afa9-74c89a72d584_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2b36-7f12-9590-9a89599035c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b36-7816-afa9-74c89a72d584" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2b36-7f12-9590-9a89599035c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2b36-7f7a-ae57-92d94e81d423" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cdd48-2b36-7f12-9590-9a89599035c4" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2b36-7f7a-ae57-92d94e81d423" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cdd48-2b36-789a-968e-f89632c1e411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_us-gaap_AwardTypeAxis_019cdd48-2b36-789a-968e-f89632c1e411" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-789a-968e-f89632c1e411_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b36-789a-968e-f89632c1e411" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-789a-968e-f89632c1e411_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-7465-aedc-8ed3c2d65143" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b36-789a-968e-f89632c1e411" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-7465-aedc-8ed3c2d65143" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OPAndLPUnitsMember_019cdd48-2b36-79bf-af4c-9ff4cdbea8cf" xlink:href="pstl-20260331.xsd#pstl_OPAndLPUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-7465-aedc-8ed3c2d65143" xlink:to="loc_pstl_OPAndLPUnitsMember_019cdd48-2b36-79bf-af4c-9ff4cdbea8cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LongTermIncentiveUnitMember_019cdd48-2b36-7ec2-8059-4bf5fc5f3944" xlink:href="pstl-20260331.xsd#pstl_LongTermIncentiveUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-7465-aedc-8ed3c2d65143" xlink:to="loc_pstl_LongTermIncentiveUnitMember_019cdd48-2b36-7ec2-8059-4bf5fc5f3944" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OPUnitsMember_019dd9ad-fc81-74be-b07b-c1d9ef3f7669" xlink:href="pstl-20260331.xsd#pstl_OPUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b36-7465-aedc-8ed3c2d65143" xlink:to="loc_pstl_OPUnitsMember_019dd9ad-fc81-74be-b07b-c1d9ef3f7669" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7034-94cd-82cc64d091cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7034-94cd-82cc64d091cc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7034-94cd-82cc64d091cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7034-94cd-82cc64d091cc" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-7034-94cd-82cc64d091cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75e2-9ca5-7eb04e4ce4b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b36-7034-94cd-82cc64d091cc" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75e2-9ca5-7eb04e4ce4b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2b36-737b-8415-908367f5ceae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2b36-75e2-9ca5-7eb04e4ce4b8" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2b36-737b-8415-908367f5ceae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019cdd48-2b36-743f-884e-b31a6e5675b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b36-772e-9caf-b5191c03e7fc" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019cdd48-2b36-743f-884e-b31a6e5675b4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019cdd48-2b36-743f-884e-b31a6e5675b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019cdd48-2b36-743f-884e-b31a6e5675b4" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019cdd48-2b36-743f-884e-b31a6e5675b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019cdd48-2b36-7ea3-85e4-d38726ebd2ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountAxis_019cdd48-2b36-743f-884e-b31a6e5675b4" xlink:to="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019cdd48-2b36-7ea3-85e4-d38726ebd2ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OperatingPartnerOPMember_019cdd48-2b36-74e7-9dee-35c26f693772" xlink:href="pstl-20260331.xsd#pstl_OperatingPartnerOPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PartnerTypeOfPartnersCapitalAccountNameDomain_019cdd48-2b36-7ea3-85e4-d38726ebd2ff" xlink:to="loc_pstl_OperatingPartnerOPMember_019cdd48-2b36-74e7-9dee-35c26f693772" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019cdd48-2b37-7569-8740-043376150406" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019cdd48-2b37-7569-8740-043376150406" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationDeferral_019cdd48-2b37-788d-8b79-ea53f3af92e6" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationDeferral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationDeferral_019cdd48-2b37-788d-8b79-ea53f3af92e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NoncontrollingInterestsOpUnits_019cdd48-2b37-78ae-85c2-511167f47319" xlink:href="pstl-20260331.xsd#pstl_NoncontrollingInterestsOpUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_NoncontrollingInterestsOpUnits_019cdd48-2b37-78ae-85c2-511167f47319" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NoncontrollingInterestLtipUnits_019cdd48-2b37-76d2-996c-804b76e2770d" xlink:href="pstl-20260331.xsd#pstl_NoncontrollingInterestLtipUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_NoncontrollingInterestLtipUnits_019cdd48-2b37-76d2-996c-804b76e2770d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OutstandingPartnershipPercentage_019cdd48-2b37-7a13-8c65-52c9861d20df" xlink:href="pstl-20260331.xsd#pstl_OutstandingPartnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_OutstandingPartnershipPercentage_019cdd48-2b37-7a13-8c65-52c9861d20df" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_CommonStockConvertibleConversionRatio_019cdd48-2b37-7e9c-abf1-0fe3d190dc7f" xlink:href="pstl-20260331.xsd#pstl_CommonStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_CommonStockConvertibleConversionRatio_019cdd48-2b37-7e9c-abf1-0fe3d190dc7f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionsInPeriod_019cdd48-2b37-788f-ba8e-2f699fd81106" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionsInPeriod_019cdd48-2b37-788f-ba8e-2f699fd81106" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountUnitsConverted_019cdd48-2b37-742f-b928-e1a4085077df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PartnersCapitalAccountUnitsConverted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_us-gaap_PartnersCapitalAccountUnitsConverted_019cdd48-2b37-742f-b928-e1a4085077df" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019cdd48-2b37-71d3-8233-44a56f12c4a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b36-7c01-82c2-d510886da421" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019cdd48-2b37-71d3-8233-44a56f12c4a4" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityRestrictedstockandotherawardsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityRestrictedstockandotherawardsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityRestrictedstockandotherawardsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7113-b71f-78e0a4d728aa" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7113-b71f-78e0a4d728aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-72aa-a693-05824333d59c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7113-b71f-78e0a4d728aa" xlink:to="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-72aa-a693-05824333d59c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-72aa-a693-05824333d59c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-72aa-a693-05824333d59c" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-72aa-a693-05824333d59c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-747e-a85e-0a803d4b516a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-72aa-a693-05824333d59c" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-747e-a85e-0a803d4b516a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeesAndConsultantsMember_019cdd48-2b37-7422-b5d9-a3e02842860d" xlink:href="pstl-20260331.xsd#pstl_EmployeesAndConsultantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-747e-a85e-0a803d4b516a" xlink:to="loc_pstl_EmployeesAndConsultantsMember_019cdd48-2b37-7422-b5d9-a3e02842860d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ManagementMember_019db722-fb2d-7870-9f08-61e3163bedc5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ManagementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-747e-a85e-0a803d4b516a" xlink:to="loc_srt_ManagementMember_019db722-fb2d-7870-9f08-61e3163bedc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-77b9-8ad9-06e02e441471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7113-b71f-78e0a4d728aa" xlink:to="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-77b9-8ad9-06e02e441471" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-77b9-8ad9-06e02e441471_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-77b9-8ad9-06e02e441471" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-77b9-8ad9-06e02e441471_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7e5f-a76b-16302c305c35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-77b9-8ad9-06e02e441471" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7e5f-a76b-16302c305c35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-78ab-a9b6-f58548f37241" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7e5f-a76b-16302c305c35" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-78ab-a9b6-f58548f37241" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019cdd48-2b37-70fc-8649-ed21542cead2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019cdd48-2b37-70fc-8649-ed21542cead2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cdd48-2b37-7759-b158-35256dabab2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cdd48-2b37-7759-b158-35256dabab2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod_019cdd48-2b37-7d22-a1a2-331ed4d172e3" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod_019cdd48-2b37-7d22-a1a2-331ed4d172e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019cdd48-2b37-7df0-8646-5044c7c90a63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019cdd48-2b37-7df0-8646-5044c7c90a63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019dd9f9-3430-735a-9a02-fab34b7e869a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019dd9f9-3430-735a-9a02-fab34b7e869a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInGeneralAndAdministrativeExpenses_019cdd48-2b37-7691-8165-d10edd86eb20" xlink:href="pstl-20260331.xsd#pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInGeneralAndAdministrativeExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInGeneralAndAdministrativeExpenses_019cdd48-2b37-7691-8165-d10edd86eb20" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInPropertyOperatingExpenses_019cdd48-2b37-7035-a39b-33a7d35c61de" xlink:href="pstl-20260331.xsd#pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInPropertyOperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_pstl_EmployeeBenefitsAndShareBasedCompensationPortionIncludedInPropertyOperatingExpenses_019cdd48-2b37-7035-a39b-33a7d35c61de" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019cdd48-2b37-7e03-b0cb-d711c2da5742" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019cdd48-2b37-7e03-b0cb-d711c2da5742" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019cdd48-2b37-7b67-af29-e5366232c239" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7d3c-9a6c-96374be8f82f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019cdd48-2b37-7b67-af29-e5366232c239" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityScheduleofunvestedsharesofrestrictedstockDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityScheduleofunvestedsharesofrestrictedstockDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityScheduleofunvestedsharesofrestrictedstockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-7c97-850c-333f32fb83b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:to="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-7c97-850c-333f32fb83b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7c97-850c-333f32fb83b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-7c97-850c-333f32fb83b1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7c97-850c-333f32fb83b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cdd48-2b37-7c97-850c-333f32fb83b1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019cdd48-2b37-768c-9322-36a2f8df45bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:to="loc_us-gaap_RestrictedStockMember_019cdd48-2b37-768c-9322-36a2f8df45bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LongTermIncentiveUnitMember_019cdd48-2b37-7427-b068-cb7194745d76" xlink:href="pstl-20260331.xsd#pstl_LongTermIncentiveUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:to="loc_pstl_LongTermIncentiveUnitMember_019cdd48-2b37-7427-b068-cb7194745d76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-7ea8-a34c-4f535d445e57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-7ea8-a34c-4f535d445e57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_MarketBasedRSUsMember_019dda10-1086-7f41-a85d-c6891095784c" xlink:href="pstl-20260331.xsd#pstl_MarketBasedRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-7ea8-a34c-4f535d445e57" xlink:to="loc_pstl_MarketBasedRSUsMember_019dda10-1086-7f41-a85d-c6891095784c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_TimeBasedRSUsMember_019dda10-9850-79e9-b17e-c0432358ea9a" xlink:href="pstl-20260331.xsd#pstl_TimeBasedRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedStockUnitsRSUMember_019cdd48-2b37-7ea8-a34c-4f535d445e57" xlink:to="loc_pstl_TimeBasedRSUsMember_019dda10-9850-79e9-b17e-c0432358ea9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PerformanceBasedRSUsMember_019dda11-0c6d-7b90-9790-b9b600c6214d" xlink:href="pstl-20260331.xsd#pstl_PerformanceBasedRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cdd48-2b37-7ede-bd6c-f8bacf3235ac" xlink:to="loc_pstl_PerformanceBasedRSUsMember_019dda11-0c6d-7b90-9790-b9b600c6214d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-73b5-8fda-1a8c99b106be" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:to="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-73b5-8fda-1a8c99b106be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-73b5-8fda-1a8c99b106be_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-73b5-8fda-1a8c99b106be" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-73b5-8fda-1a8c99b106be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019cdd48-2b37-73b5-8fda-1a8c99b106be" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b37-75e6-aada-462e3cef2b6c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:to="loc_srt_ChiefExecutiveOfficerMember_019cdd48-2b37-75e6-aada-462e3cef2b6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PresidentMember_019cdd48-2b37-7f6b-97cf-43d86a0de740" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_PresidentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:to="loc_srt_PresidentMember_019cdd48-2b37-7f6b-97cf-43d86a0de740" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeeMember_019cdd48-2b37-7b41-8201-5e1e07f19bdf" xlink:href="pstl-20260331.xsd#pstl_EmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:to="loc_pstl_EmployeeMember_019cdd48-2b37-7b41-8201-5e1e07f19bdf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_CertainOfficersAndEmployeesMember_019dda44-a688-72e6-84c6-ff4de127c123" xlink:href="pstl-20260331.xsd#pstl_CertainOfficersAndEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:to="loc_pstl_CertainOfficersAndEmployeesMember_019dda44-a688-72e6-84c6-ff4de127c123" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_OfficersAndEmployeeMember_019cdd48-2b37-7a3e-8c1f-dc68d01219d8" xlink:href="pstl-20260331.xsd#pstl_OfficersAndEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cdd48-2b37-7c2f-acab-b718b4f7886c" xlink:to="loc_pstl_OfficersAndEmployeeMember_019cdd48-2b37-7a3e-8c1f-dc68d01219d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019cdd48-2b37-73b6-9f58-fae5f9362d77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:to="loc_us-gaap_VestingAxis_019cdd48-2b37-73b6-9f58-fae5f9362d77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019cdd48-2b37-73b6-9f58-fae5f9362d77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019cdd48-2b37-73b6-9f58-fae5f9362d77" xlink:to="loc_us-gaap_VestingDomain_019cdd48-2b37-73b6-9f58-fae5f9362d77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019cdd48-2b37-7d5e-b10c-8ab9b477bb81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019cdd48-2b37-73b6-9f58-fae5f9362d77" xlink:to="loc_us-gaap_VestingDomain_019cdd48-2b37-7d5e-b10c-8ab9b477bb81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019cdd48-2b37-7eb2-8a31-20392cede444" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019cdd48-2b37-7d5e-b10c-8ab9b477bb81" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019cdd48-2b37-7eb2-8a31-20392cede444" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019cdd48-2b37-7c20-afb8-e076a03aa350" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019cdd48-2b37-7d5e-b10c-8ab9b477bb81" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019cdd48-2b37-7c20-afb8-e076a03aa350" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019cdd48-2b37-7aa7-a32c-0479f650d23c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019cdd48-2b37-7d5e-b10c-8ab9b477bb81" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019cdd48-2b37-7aa7-a32c-0479f650d23c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019cdd48-2b37-7819-b986-f6049f76795d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:to="loc_us-gaap_PlanNameAxis_019cdd48-2b37-7819-b986-f6049f76795d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b37-7819-b986-f6049f76795d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b37-7819-b986-f6049f76795d" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b37-7819-b986-f6049f76795d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b37-7156-9bb5-5632662343c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b37-7819-b986-f6049f76795d" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b37-7156-9bb5-5632662343c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_LongTermIncentivePlanMember_019cdd48-2b37-7e0e-b64c-d76bf58ababd" xlink:href="pstl-20260331.xsd#pstl_LongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019cdd48-2b37-7156-9bb5-5632662343c1" xlink:to="loc_pstl_LongTermIncentivePlanMember_019cdd48-2b37-7e0e-b64c-d76bf58ababd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockTable_019cdd48-2b37-7173-b7ac-e629a75d95ba" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cdd48-2b37-7c34-8cff-354f9943261c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cdd48-2b37-7e9e-9cc0-5f64f5540fcc" xlink:to="loc_us-gaap_EquityComponentDomain_019cdd48-2b37-7c34-8cff-354f9943261c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2b37-71df-a942-95795544284b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cdd48-2b37-7c34-8cff-354f9943261c" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019cdd48-2b37-71df-a942-95795544284b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cdd48-2b37-7a0c-a936-e323082dcf58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cdd48-2b37-7a0c-a936-e323082dcf58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cdd48-2b37-779f-a2a8-a06311659c69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cdd48-2b37-779f-a2a8-a06311659c69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriod_019dd9f6-8c08-7201-aa47-74dd858c9040" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriod_019dd9f6-8c08-7201-aa47-74dd858c9040" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019cdd48-2b37-7442-8e80-33c4130ecfa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_019cdd48-2b37-7442-8e80-33c4130ecfa5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019cdd48-2b37-7ff4-b7cc-6c58d81c4d9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019cdd48-2b37-7d6b-b6c7-f3547226acd3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019cdd48-2b37-7ff4-b7cc-6c58d81c4d9f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cdd48-2b37-7eea-b515-832462631536" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cdd48-2b37-79a1-8a08-bf86739ccb5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cdd48-2b37-79a1-8a08-bf86739ccb5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019cdd48-2b37-7044-a33d-3ebc4f074194" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019cdd48-2b37-7044-a33d-3ebc4f074194" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriodWeightedAverageGrantDateFairValue_019dd9fd-ff60-7843-92b9-e7813379ed99" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedInPeriodWeightedAverageGrantDateFairValue_019dd9fd-ff60-7843-92b9-e7813379ed99" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionToCommonStockWeightedAveragePricePerShare_019cdd48-2b37-71c0-9aa5-1cf1a626acd2" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionToCommonStockWeightedAveragePricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionToCommonStockWeightedAveragePricePerShare_019cdd48-2b37-71c0-9aa5-1cf1a626acd2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019cdd48-2b37-7efa-b524-2cc940abff65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cdd48-2b37-7c7a-a139-070bb36f7414" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019cdd48-2b37-7efa-b524-2cc940abff65" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cdd48-2b37-781e-8f3b-345566e055bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingNumber_019dda06-3165-71a0-b5ab-0219344f5135" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingNumber_019dda06-3165-71a0-b5ab-0219344f5135" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019dda03-e5e1-7ea1-9f71-dab194ff3943" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019dda03-e5e1-7ea1-9f71-dab194ff3943" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019cdd48-2b37-7ebf-a1ed-f64458a187d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019cdd48-2b37-7ebf-a1ed-f64458a187d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_019cdd48-2b37-7e7b-bf93-5670dc7eb13f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_019cdd48-2b37-7e7b-bf93-5670dc7eb13f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod_019dda0c-ad40-7d0b-86f0-97c62da9cbe5" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod_019dda0c-ad40-7d0b-86f0-97c62da9cbe5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformanceTargetEarnedPercentage_019dda27-b8c7-78fe-b14e-a88bfac2ec9f" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformanceTargetEarnedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_pstl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformanceTargetEarnedPercentage_019dda27-b8c7-78fe-b14e-a88bfac2ec9f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019cdd48-2b37-7d1c-90f5-671d2e6dda7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019cdd48-2b37-7d1c-90f5-671d2e6dda7a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_ShareBasedCompensationArrangementWithheldRestrictedShares_019cdd48-2b37-7410-9530-9d6814c3e2fb" xlink:href="pstl-20260331.xsd#pstl_ShareBasedCompensationArrangementWithheldRestrictedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsScheduleofunvestedsharesofrestrictedstockLineItems_019cdd48-2b37-70a0-ad6c-379710a90d82" xlink:to="loc_pstl_ShareBasedCompensationArrangementWithheldRestrictedShares_019cdd48-2b37-7410-9530-9d6814c3e2fb" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/StockholdersEquityEmployeestockpurchaseplanDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#StockholdersEquityEmployeestockpurchaseplanDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/StockholdersEquityEmployeestockpurchaseplanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7bd4-953b-a441eadbc0cd" xlink:href="pstl-20260331.xsd#pstl_StockholdersEquityDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:to="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7bd4-953b-a441eadbc0cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019cdd48-2b37-72b7-857a-5b7c0784e83d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7bd4-953b-a441eadbc0cd" xlink:to="loc_us-gaap_PlanNameAxis_019cdd48-2b37-72b7-857a-5b7c0784e83d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b37-72b7-857a-5b7c0784e83d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b37-72b7-857a-5b7c0784e83d" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b37-72b7-857a-5b7c0784e83d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019cdd48-2b37-763d-b0c4-f45d35ac1eea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019cdd48-2b37-72b7-857a-5b7c0784e83d" xlink:to="loc_us-gaap_PlanNameDomain_019cdd48-2b37-763d-b0c4-f45d35ac1eea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_EmployeeStockPurchasePlanMember_019cdd48-2b37-7a8c-a56e-6494098cf7a5" xlink:href="pstl-20260331.xsd#pstl_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019cdd48-2b37-763d-b0c4-f45d35ac1eea" xlink:to="loc_pstl_EmployeeStockPurchasePlanMember_019cdd48-2b37-7a8c-a56e-6494098cf7a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b37-7d89-ad8a-c30690c1899f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pstl_StockholdersEquityDetailsTable_019cdd48-2b37-7bd4-953b-a441eadbc0cd" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b37-7d89-ad8a-c30690c1899f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b37-7d89-ad8a-c30690c1899f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b37-7d89-ad8a-c30690c1899f" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b37-7d89-ad8a-c30690c1899f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019cdd48-2b37-7d61-8258-25c9ed037609" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019cdd48-2b37-7d89-ad8a-c30690c1899f" xlink:to="loc_us-gaap_ClassOfStockDomain_019cdd48-2b37-7d61-8258-25c9ed037609" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019cdd48-2b37-7362-9d2b-a3e0f35b1a2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019cdd48-2b37-7d61-8258-25c9ed037609" xlink:to="loc_us-gaap_CommonClassAMember_019cdd48-2b37-7362-9d2b-a3e0f35b1a2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019cdd48-2b37-745e-891f-6df4b68e3f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019cdd48-2b37-745e-891f-6df4b68e3f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_019cdd48-2b37-7bd7-a0a2-f061f959f737" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_019cdd48-2b37-7bd7-a0a2-f061f959f737" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019cdd48-2b37-7199-a54b-b6d47701a0dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:to="loc_us-gaap_SharesIssued_019cdd48-2b37-7199-a54b-b6d47701a0dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_RecognizedCompensationExpense_019cdd48-2b37-73eb-a21a-632bd63f18dd" xlink:href="pstl-20260331.xsd#pstl_RecognizedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pstl_StockholdersEquityDetailsLineItems_019cdd48-2b37-7c01-ab04-768df942b305" xlink:to="loc_pstl_RecognizedCompensationExpense_019cdd48-2b37-73eb-a21a-632bd63f18dd" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://postalrealtytrust.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="pstl-20260331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://postalrealtytrust.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019cdd48-2b37-7929-8f98-19668d16d589" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019cdd48-2b37-7929-8f98-19668d16d589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019cdd48-2b37-7929-8f98-19668d16d589_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019cdd48-2b37-7929-8f98-19668d16d589" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019cdd48-2b37-7929-8f98-19668d16d589_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019cdd48-2b37-7907-8cde-8cd252de7fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019cdd48-2b37-7929-8f98-19668d16d589" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019cdd48-2b37-7907-8cde-8cd252de7fdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019cdd48-2b37-7cb3-99ea-9b1bd220f3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019cdd48-2b37-7907-8cde-8cd252de7fdf" xlink:to="loc_us-gaap_SubsequentEventMember_019cdd48-2b37-7cb3-99ea-9b1bd220f3e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019cdd48-2b37-7748-9cde-44355c950271" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:to="loc_us-gaap_CreditFacilityAxis_019cdd48-2b37-7748-9cde-44355c950271" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b37-7748-9cde-44355c950271_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b37-7748-9cde-44355c950271" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b37-7748-9cde-44355c950271_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cdd48-2b37-7b6e-9df8-179f93e64ecf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019cdd48-2b37-7748-9cde-44355c950271" xlink:to="loc_us-gaap_CreditFacilityDomain_019cdd48-2b37-7b6e-9df8-179f93e64ecf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b37-7119-82e3-49486eddb2f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cdd48-2b37-7b6e-9df8-179f93e64ecf" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cdd48-2b37-7119-82e3-49486eddb2f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b37-717c-9979-4568979bb2f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cdd48-2b37-7c7e-86e3-1cd14b1b56c5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b37-717c-9979-4568979bb2f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019cdd48-2b37-7743-be54-8ec76b3babbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cdd48-2b37-717c-9979-4568979bb2f4" xlink:to="loc_us-gaap_LineOfCreditMember_019cdd48-2b37-7743-be54-8ec76b3babbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019def58-7fad-7df3-a0c7-0ecf54f5636b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019cdd48-2b37-7887-a6d6-efe8e5318476" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019def58-7fad-7df3-a0c7-0ecf54f5636b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019def58-7fad-7df3-a0c7-0ecf54f5636b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019def58-7fad-7df3-a0c7-0ecf54f5636b" xlink:to="loc_us-gaap_ClassOfStockDomain_019def58-7fad-7df3-a0c7-0ecf54f5636b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019def58-7fad-7db4-b4d9-825df4e38aef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019def58-7fad-7df3-a0c7-0ecf54f5636b" xlink:to="loc_us-gaap_ClassOfStockDomain_019def58-7fad-7db4-b4d9-825df4e38aef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019def58-92b6-7685-9b58-4a258a9e999c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019def58-7fad-7db4-b4d9-825df4e38aef" xlink:to="loc_us-gaap_CommonClassAMember_019def58-92b6-7685-9b58-4a258a9e999c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019cdd48-2b37-795e-8e9c-d82ec9e850f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019cdd48-2b37-795e-8e9c-d82ec9e850f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019cdd48-2b37-7199-941d-97be3bf2ac5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_us-gaap_LongTermDebt_019cdd48-2b37-7199-941d-97be3bf2ac5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPostalPropertiesAcquired_019cdd48-2b37-770d-9d7c-9b343f4b4a42" xlink:href="pstl-20260331.xsd#pstl_NumberOfPostalPropertiesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_pstl_NumberOfPostalPropertiesAcquired_019cdd48-2b37-770d-9d7c-9b343f4b4a42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019cdd48-2b37-79f3-b710-b48515e131e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019cdd48-2b37-79f3-b710-b48515e131e8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019def58-d7f4-71f0-8df3-67d345e10a27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019def58-d7f4-71f0-8df3-67d345e10a27" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_NumberOfPostalPropertiesToBeAcquired_019cdd48-2b37-7a38-9225-a805ba1f0141" xlink:href="pstl-20260331.xsd#pstl_NumberOfPostalPropertiesToBeAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_pstl_NumberOfPostalPropertiesToBeAcquired_019cdd48-2b37-7a38-9225-a805ba1f0141" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_PurchaseOfPropertyPlantAndEquipmentEstimatedCost_019cdd48-2b37-792a-9683-d5233b0e6a6f" xlink:href="pstl-20260331.xsd#pstl_PurchaseOfPropertyPlantAndEquipmentEstimatedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019cdd48-2b37-7335-b776-809540c10332" xlink:to="loc_pstl_PurchaseOfPropertyPlantAndEquipmentEstimatedCost_019cdd48-2b37-792a-9683-d5233b0e6a6f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilities" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndOtherAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilities" xlink:type="arc" order="31"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_pstl_AndrewSpodekMember_019cdd48-29aa-7243-8a3c-afaeae6f62fe" xlink:href="pstl-20260331.xsd#pstl_AndrewSpodekMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pstl_AndrewSpodekMember_019cdd48-29aa-7243-8a3c-afaeae6f62fe" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
