Address Types
How to address an envelope to a PO Box
Write PO BOX and the number on its own line, directly above the city line, with no other address on the envelope. Do not include a street address as well. When an envelope has both, the Postal Service delivers to whichever one sits on the line just above the city, and the other one is ignored.
Checked July 30, 2026/7 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page7 sections
A post office box looks like the simplest address there is, and it mostly is. One line, one number. The trouble starts when an envelope carries a box number and a street address at the same time.
That happens more than you would think. A business card lists both. Someone copies the whole block into a label. Now the envelope has two places it could go, and the Postal Service has a rule for picking: whatever sits on the line right above the city line wins. Everything else is treated as a note.
A PO Box also behaves differently from a street address in ways that have nothing to do with formatting. It belongs to the post office itself, not to a building, so it has no fixed relationship to the ZIP code of the street it happens to sit on, it can be rented by more than one person, and by policy it cannot receive anything from a private courier the way a street address can. None of that shows up by looking at the envelope. All of it shapes how the address should actually be written, and it is why a page that only repeats the plain box format misses half of what a real PO Box holder runs into.
Step by step
Use the plain box format
PO BOX, a space, then the number. No pound sign, no periods, nothing else on that line.
A MERCERPO BOX 4120ITHACA NY 14850CorrectThe whole address. Nothing is missing. Leave the street address off
If someone gives you both a street address and a box, pick the box and drop the street. Two delivery lines on one envelope is the most common reason box mail goes astray.
A MERCER88 PINE GROVE RDPO BOX 4120ITHACA NY 14850What was writtenThe street line sits above the box, so the box is what gets used and the street is dead weight. Check the ZIP against the box, not the town
Post office boxes often sit in their own ZIP code, separate from the street ZIP for the same town. Use the ZIP the box owner gave you.
Know when it is PMB instead
A private mailbox at a store like the UPS Store is a PMB, not a PO Box. It uses the store street address with PMB and the number at the end of the street line.
A MERCER210 COMMERCE ST PMB 118ITHACA NY 14850CorrectA private mailbox. Street address, PMB last. Register a street address at the post office if you need UPS or FedEx delivery
USPS offers a real fix for box holders who need courier delivery: the post office can assign your box a physical street-style address, written as your box number after a pound sign at the actual post office street address. Ask the counter staff for this if a sender insists on shipping UPS or FedEx to you.
A MERCER500 W STATE STITHACA NY 14850CorrectThe street-addressing workaround, used only when a courier needs it.
A few real examples
The steps above cover the rule. These show it applied to a spread of real situations, so you can match yours to the closest one.
Quick reference
| Box type | Format | Where it lives |
|---|---|---|
| Post office box | PO BOX 4120 | Inside a post office |
| Private mailbox | 210 COMMERCE ST PMB 118 | A retail store |
| Both given to you | Use the PO Box only | Pick one, never both |
| Need UPS/FedEx delivery | Street-style address from the post office | Ask the counter staff to assign one |
Special cases
The rule above covers most people. Here is what changes for the rest.
Can two people share the same PO Box?
Yes, and both names can go on mail addressed to it. Write each name the way you normally would, either on separate pieces of mail or, for a joint letter, both names on the name line separated by "and."
How do I use my PO Box as a return address?
The same format as the delivery address: your name, PO BOX and the number, then city, state and ZIP. There is no different rule for a box used as a return address versus a delivery address.
Why did my package get returned even though I addressed it to my PO Box correctly?
Most likely the sender used UPS or FedEx, neither of which can deliver to a plain PO Box format at all, regardless of how correctly it is written. This is the single most common reason correctly formatted PO Box mail still fails, and the street-addressing workaround above is the fix.
Key terms on this page
- PO Box
- A physical mailbox inside a post office, rented from and operated entirely by USPS. Only USPS can deliver to it directly.
- PMB
- Private Mailbox, a numbered box at a real street address run by a commercial mail receiving agency, such as a UPS Store. Because it has a real street address behind it, any courier can deliver there.
- CMRA
- Commercial Mail Receiving Agency, the type of business that rents out PMBs. Regulated separately from USPS, which is why a PMB address looks and behaves differently from a PO Box.
- Street-addressing workaround
- A service some post offices offer that assigns a PO Box a physical street-style address, so couriers who cannot deliver to a plain box number can still reach it.