PO Box only Zip Codes
Jan 25, 2024

PO Box only Zip Codes

ZIP codes are an important component of an address, they allow postal services to easily identify and sort mail pieces sent for delivery. Excluding a ZIP code from an address could cause delays, and would require resources to be delivered to the correct destination.

What are PO Box-Only ZIP Codes?

There are some circumstances when an address does not have a mailbox but they may still require access to the postal services. These addresses without mailboxes are called PO Box only ZIP codes, they only contain a PO Box address.

Each ZIP code includes a classification indicator, and the PO box addresses are classified as “P.” This makes it easy for the USPS to filter out addresses that they do not deliver mail to the physical addresses.



When an address is deliverable, it is classified as "S" which stands for Standard. This could. include an office or a home, as long as postal mail can be delivered to the physical address.


Another classification is "M", which stands for "Military". These are addresses that are American by nationality, but not if you consider them by the locality. Examples of such addresses are ships that are stationary or military installations. The military addresses are deliverable but require delivery system similar to international shipping


Some addresses are classified as "U" or Unique. They include companies, organizations, and institutions that receive a large number of mail pieces.

PO Box

The final classification is "P" for PO boxes, which are addresses that cannot receive mail directly. Any home or business location is listed under this classification.

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