A counter pickup slip
USPS's own wording: "Get a slip to pick them up from the counter during normal business hours." The box holder finds a note where the letters usually go.
Priority Mail
Yes, Priority Mail reaches every PO Box
The rule sits in one line of the Domestic Mail Manual: a box customer receives any mail properly addressed to the box number. Priority Mail is USPS's own product, so there's no carrier hand-off to question and no separate exception written anywhere. What actually varies is whether the box itself is big enough — and USPS builds its box sizes around exactly that question. Rules below read at pe.usps.com and usps.com on 2026-08-28.
DMM 508.4.3 citedRead 2026-08-28Berkeley Heights, NJ
The box number is the whole address
Skip the street line. USPS's manual is specific about what goes where on a PO Box piece.
Where the "yes" comes from
Any individual box customer or organization may receive through the box any mail properly addressed to the box number. Domestic Mail Manual 508.4.3.1, pe.usps.com, read 2026-08-28.
There's no class-by-class exception list attached to that sentence, and Priority Mail is not a separate carrier riding on USPS's network the way UPS Ground Saver or FedEx Ground Economy do — it is USPS. So the question that actually decides your experience isn't whether it's allowed; it's whether the specific box a customer rents can physically hold what arrives.
USPS sizes its boxes around Priority Mail
This is the detail most PO Box explainers miss: usps.com's own box-rental page, read 2026-08-28, describes its lobby box sizes in terms of Priority Mail Flat Rate packaging, not just letters.
| Box size | What USPS says it holds |
|---|---|
| Extra Small | 10-15 letters and 3 rolled magazines |
| Size 2 | 15+ letters, 5 rolled magazines, or 1 Small Priority Mail Flat Rate Box |
| Larger sizes | Described as fitting Small and Medium Priority Mail Flat Rate Boxes |
| Extra Large | "Big enough for multiple packages" |
A Large Flat Rate Box, a Regional Rate Box, or anything oversized will not slide through most lobby doors regardless of the rental tier. That is not a delivery failure; it is a size mismatch, and the next section is what USPS actually does about it.
When the package outgrows the box
Per usps.com/manage/po-boxes.htm, read 2026-08-28, a parcel too large for the box goes one of two ways, and either one still reaches the recipient without going back to the sender.
A secure parcel locker
Or: "Get your package from a secure parcel locker (including USPS Smart Lockers at select locations) at your convenience" — no counter hours to work around.
Addressing, unchanged
DMM 508.4.1.4 puts the box number on the line directly above city, state and ZIP. No street address, no unit number for the box itself.
Where the other carriers stand
UPS and FedEx don't sell PO Box delivery as a rule — they sell it through exactly one product each that hands the last mile to USPS: UPS Ground Saver and FedEx Ground Economy. Their faster tiers, along with plain UPS Ground and overnight service, still want a street address. Priority Mail Express, the USPS overnight product, reaches a PO Box the same way ordinary Priority Mail does, with delivery by 6 PM on its published 1-3 day window. The full carrier-by-carrier breakdown, with a live quoted example, is on our PO Box shipping guide.
Price a parcel to a PO Box Priority Mail Flat Rate envelopes
Common questions
Can you send Priority Mail to a PO Box?
Yes. Domestic Mail Manual 508.4.3.1, read 2026-08-28, says a box customer may receive through the box any mail properly addressed to the box number, with no carve-out for Priority Mail or any other USPS class. It is the one delivery point every USPS service reaches without exception.
Will a Priority Mail Flat Rate Box actually fit in a small PO Box?
USPS sizes its own boxes around the answer. Per usps.com, read 2026-08-28, its size 2 PO Box holds 15+ letters, 5 rolled magazines, or 1 Small Priority Mail Flat Rate Box, and its larger sizes are described as fitting Small and Medium Flat Rate Boxes. A Large Flat Rate Box or a bulky Regional Rate box is a different question, covered below.
What happens if the Priority Mail box is too big for the PO Box?
It still gets delivered. USPS's PO Box page, read 2026-08-28, says a package that doesn't fit either gets a slip to pick it up from the counter during normal business hours, or goes into a secure parcel locker, including USPS Smart Lockers at select locations, for the holder to collect at their convenience.
How do I address Priority Mail for a PO Box?
Per Domestic Mail Manual 508.4.1.4, read 2026-08-28: the assigned PO Box number goes in the address immediately above the city, state and ZIP code. Skip the street address unless the holder has separately arranged street addressing with their Post Office.
How fast is Priority Mail to a PO Box?
The same 2-3 day window USPS publishes for Priority Mail generally, per usps.com read 2026-08-28. A PO Box changes the last few feet of delivery, not the transit standard.
Can UPS or FedEx reach a PO Box the way Priority Mail can?
Only through the one product each hands off to USPS for the last mile — UPS Ground Saver and FedEx Ground Economy. Their faster, non-economy services still require a street address, which our full PO Box guide covers in detail.