US PO Box address format

How a US PO Box address is written, and why checkout still sees other spellings

Direct answer. USPS Publication 28, section 281, says the Post Office Box address on a mailpiece must be standardized as PO BOX ##, where “##” indicates the actual number, numbers, or letter. That standardized line has no periods. Section 222 says that, with the exception of the hyphen in the ZIP+4 Code, punctuation may be omitted in the delivery address block, and that no punctuation is preferred. Section 284 says PO Box services in some locations allow an option to use the Post Office street address for the mailing address, along with the PO Box number preceded by a “#” sign or “UNIT” designation. usps.com calls that option Street Addressing, subject to availability and restrictions. Shoppers still type “P.O. Box”, “Post Office Box”, “POB”, “Box 12”, and locker lines. A checkout rule that matches only one of those strings will miss the others. The spelling test list is a separate page. This page is not legal advice.

PO Box Blocker — AddressFence (Shopify App Store · Write a review). Free blocks PO Boxes and parcel lockers on the shipping address at checkout, plus a small set of ZIP rules. Street-number checks and billing-address rules are on a paid plan. It lets you test any address in the simulator before publishing, with one-click rollback. This page is the USPS format reading aid — not a list of every string the app matches.

Related: B2B PO Guard — Require PO — B2B purchase order number required at company checkout.

Free check first: PO box and street number address checker runs in your browser and sends nothing. Paste addresses and see which look like a PO box or lack a street number.

Checklist before you write the line or the rule

• Read Publication 28, section 281, for the standardized “PO BOX” plus the number.
• Read section 283 for designations the Postal Service says to change to PO BOX on output.
• Read section 222 before you treat punctuation as forbidden. The preferred form omits it, except the ZIP+4 hyphen.
• Read section 284 and the usps.com PO Box page before you describe Street Addressing. It is an option in some locations, not a format every box has.
• For the checkout spellings shoppers actually type, use the spelling-variants test list. This page does not repeat that list.

The standardized mailpiece line

Section 281 is titled Format, under “28 Post Office Box Addresses”. The sentence is: “The Post Office Box address on a mailpiece must be standardized as follows: PO BOX ## (in this example, ‘##’ indicates the actual number, numbers, or letter).” That is the delivery-address form Publication 28 standardizes. It is not “P.O. Box”, “Post Office Box”, or “POB”.

Section 282 says Post Office Box numbers that are preceded by significant leading zeroes are identified in the ZIP+4 file by a hyphen preceding the box number, and that the hyphen is converted into a zero on the output mailpiece. Section 283 says PO Box addresses often appear with the word CALLER, FIRM CALLER, BIN, LOCKBOX, or DRAWER, and that those designations are changed to PO BOX as output on a mailpiece.

Section 222, under the last line of the address, says punctuation may be omitted in the delivery address block except for the hyphen in the ZIP+4 Code, that an address with punctuation is acceptable, and that an address with no punctuation is preferred. The standardized “PO BOX” token in section 281 is already written without periods.

Street Addressing, where the Post Office offers it

Publication 28 section 284 is titled “PO Box Street Addressing”. It says PO Box services in some locations allow an option to use the Post Office street address for the mailing address, along with the PO Box number preceded by a “#” sign or “UNIT” designation. The usps.com PO Box page lists Street Addressing among PO Box features: a delivery address for packages from other carriers, including Amazon, DHL, FedEx, and UPS, subject to availability and restrictions. The same page’s question “What is Street Addressing and how can I get it for my PO Box?” says that, if available, you have the option of using the street address of your Post Office location, combined with your PO Box number, as your mailing address, so you can receive packages from private carriers such as UPS, FedEx, DHL, and Amazon, as long as they comply with USPS mailing standards. It points to the customer agreement for details. A street-style line can still be a PO Box. Whether a given box has the option is a location question on those USPS pages, not a guess from the words “PO BOX”.

Why the checkout line does not match section 281

People ordering online type the words they say: “P.O. Box”, “Post Office Box”, “POB”, a bare “Box 12”, or a locker line. Publication 28 tells mailers to standardize those kinds of designations to PO BOX on the mailpiece. A shopper at checkout has not done that. A rule that looks only for the letters P, O, space, B, O, X will miss “Post Office Box” and can also be confused by a real street. The strings to paste, and the look-alike streets to keep, are on PO box spellings and look-alike street names. Run them in the simulator before you publish.

Whether a carrier will deliver to a PO Box is a different question: Does Shopify ship to PO Boxes? Billing is a different surface from shipping: PO box blocker for the billing address. APO, FPO, and DPO lines are not PO Boxes: Shopify APO, FPO, and DPO addresses.

What this page is not

• Not legal advice, a carrier rule, or a card-network rule.
• Not a substitute for the live Publication 28 sections or the usps.com PO Box page.
• Not the spelling test list. That URL is PO box spellings and look-alike street names.
• Not a Canada Post or Australia Post format. This page does not describe those.

Related pages

• PO box and street number address checker — paste lines and see which look like a PO box
• PO box spellings and look-alike street names — the test list for a checkout rule
• Is a PO Box a physical address? — the Post Office mailbox, Street Addressing, and the CAN-SPAM footer
• Does Shopify ship to PO Boxes?
• PO box blocker
• PO box blocker for the billing address
• Shopify APO, FPO, and DPO addresses
• Publication 28, section 281 — PO BOX format
• Publication 28, section 284 — PO Box Street Addressing
• usps.com: Rent a PO Box — Street Addressing, subject to availability
• PO Box Blocker — AddressFence — live App Store listing
• Shopify apps hub
• Tools

Not legal advice. Confirm Publication 28 sections 222, 281, 283, and 284, and the usps.com PO Box page, before you treat an address line as a standardized PO Box or as Street Addressing. The app checks address rules you publish. It does not decide carrier eligibility.