What is a PO Box ZIP code

Mar 3, 2026

Updated: March 3, 2026

What is a PO Box ZIP code refers to the ZIP code assigned by USPS for mail delivered to post office boxes at a specific post office location. This ZIP code may be different from, or the same as, the ZIP code used for nearby street addresses.

In some areas, USPS assigns a unique ZIP code exclusively for PO Box delivery to route mail directly to the correct post office. In other locations, PO Boxes and street addresses share the same ZIP code.

A PO Box ZIP code is valid only when used with a PO Box address. Using a PO Box ZIP code with a street address, or vice versa, can cause address validation errors or misrouting.

Because PO Box ZIP code usage depends on local USPS configuration, address systems must distinguish between PO Box and street-based addresses before applying ZIP code rules.

Clear separation of PO Box and street address logic improves validation accuracy and prevents delivery issues in mailing and shipping workflows.

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