LetterAgent
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Home > Guides > Mailing to a PO box
Yes: letters to PO boxes are completely routine. Put the recipient's name on the first line, the PO box number on its own line where the street address would normally go, then the city, state or province, and ZIP or postal code. Postage costs the same as a street-address letter.
The box number takes the place of the street address: it gets its own line, and you leave the street address off entirely. Don't combine them ("123 Main St, PO Box 456" confuses sorting equipment; the machines read the line directly above the city first, so put the PO box there). Write it out as "PO Box 456": abbreviations like "P.O. Box" or "P O Box" work, but the plain version is what postal software expects.
| Destination | Format |
|---|---|
| US PO box | Jane Smith PO Box 456 Springfield, IL 62701 |
| Canadian PO box | Jane Smith PO Box 456 Springfield ON K1A 0B1 |
| Private mailbox (e.g. UPS Store) | Jane Smith 123 Main St, PMB 456 Springfield, IL 62701 |
Here's something most people don't know: at many post offices, a PO box holder can also receive mail addressed in street style: the post office's own street address plus their box number, like "123 Main St #456." USPS calls this Street Addressing, and it's meant for private carriers: FedEx and UPS can't deliver to a "PO Box," so box holders at participating post offices get a street-style address they can hand to any carrier. Not every post office offers it, though: it depends on the location, so if someone gives you a street-style address for their box, use exactly what they gave you and don't try to convert it yourself.
One detail that trips people up: some senders try to be clever and address a letter to both the street address and the PO box. Don't. If the recipient's mail is held at the box, the box line should be the delivery line. Automated sorters read bottom-up, so whichever line sits directly above the city/state/ZIP line is treated as the address that counts.
Private mailbox services (UPS Store, Mail Boxes Etc., and independent pack-and-ship shops) are commercial mail receiving agencies, and they have their own strict format. The address uses the store's street address, and the box is identified with a PMB (private mailbox) designator: "PMB 456" or "#456." USPS requires the PMB wording on mail sent through its system to these addresses.
This is where formatting mistakes actually cause bounces. Writing "Suite 456" or "Apt 456" instead of "PMB 456" can get the letter misrouted or returned, because the carrier reads it as a separate unit in the building rather than a box at the mail counter. When in doubt, copy the address exactly as the recipient wrote it: they've usually learned the hard way which version works.
Yes. Certified mail to a US PO box works normally: the recipient gets a delivery notice in their box and signs for the letter at the counter. Canada Registered Mail to a PO box works the same way. The signature happens at the post office counter instead of a doorstep, but the proof of delivery is identical. If you're sending something where proof matters, a PO box destination is no obstacle.
Yes. A PO box address goes through LetterAgent exactly like a street address: give your assistant the recipient's name, the PO box line, and the city, state or province, and ZIP or postal code, and it's printed and mailed the same way. PO boxes accept standard letters with no surcharge, so pricing works exactly as quoted.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it's printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
Need help? Ask your assistant: it can check a job's status any time. If it ever can't handle something: hello@getletteragent.com