Sending something to a PO Box is not more complicated than sending it to a house. It is just different in one specific way, and that one difference is what trips people up.
Letters and small packages work exactly like they would anywhere else. The catch only shows up with certain carriers and certain package sizes.
Knowing that one difference in advance answers most of how to send mail to a PO Box without any guessing.
How to send mail to a PO Box: letters and small envelopes
Standard mail works without any special steps. Address the envelope with the recipient’s name, then PO BOX and the number.
Add the city, state, and ZIP code on the next line. Drop it in any mailbox or hand it to a clerk, exactly like mail to a house.
USPS treats a PO Box as a completely normal delivery point for letters. For the exact line by line format, see our guide to writing a PO Box address.
Sending accountable mail: certified, insured, or signature required
Certified mail, insured mail, and other accountable services all work at a PO Box. These require a signature, so the recipient collects them at the counter instead of finding them in the box.
A notice slip appears in the box telling the recipient a signature item is waiting. From there, the process looks the same as it does for any address in the country.
Shipping a package through USPS
USPS packages, including Priority Mail and Ground Advantage, deliver to a PO Box the same way letters do. Small packages fit directly in the box.
Oversized ones trigger a pickup notice or a parcel locker key instead. There is no special step for the sender here either, so address it the same way you would a letter.
Shipping a package through UPS, FedEx, or DHL
This is the one real catch in how to send mail to a PO Box using a private carrier. UPS, FedEx, and DHL Express all require a genuine street address to complete a delivery.
A plain PO Box does not qualify on its own. The recipient needs USPS Street Addressing set up on their box first, which gives it a real street address these carriers can deliver to.
See our guide to PO Box Street Addressing for what that looks like from the recipient’s side. If you are the sender, simply ask them for that version of their address before you book the shipment.
What to do if you only have a plain PO Box address
Ask the recipient directly whether their box has Street Addressing enabled. Most people who rely on a PO Box for deliveries already know this.
They can usually give you the correct format right away. If they are unsure, point them to our guide on UPS delivery to a PO Box or FedEx PO Box shipping.
Switching the shipment to USPS instead is the other simple fix. A plain PO Box always accepts USPS deliveries with no setup required.
Package size limits to keep in mind
Even with Street Addressing, most competitive locations cap packages around 70 pounds. The combined length and girth limit runs about 130 inches.
Freight and oversized shipments still will not fit through this option. For anything close to that limit, our dimensional weight calculator helps confirm whether a package will be accepted.
Frequently asked questions
Can you send a package to a PO Box?
Yes, through USPS without any special setup. UPS, FedEx, and DHL Express need the recipient to have Street Addressing enabled first.
How do you send a letter to a PO Box?
Address it exactly like a letter to a house, using the recipient’s name, PO BOX and the number, then city, state, and ZIP. Drop it in any mailbox or hand it to a clerk.
Can you send certified mail to a PO Box?
Yes. The recipient collects it at the counter with a signature instead of finding it directly in the box, but the process otherwise works like any other address.
Why did my UPS or FedEx shipment get rejected for a PO Box address?
Those carriers require a real street address to complete delivery. The recipient needs USPS Street Addressing enabled so their box has one.
Can you send priority mail to a PO Box?
Yes. Priority Mail is a USPS service. It delivers to a PO Box the same way any other USPS mail does.
Is there anything you cannot send to a PO Box at all?
Freight and packages beyond the size and weight limits of the location will not fit, even with Street Addressing enabled. Most ordinary letters and packages go through without issue.
The bottom line
How to send mail to a PO Box comes down to one distinction. Letters, certified mail, and anything shipped through USPS work exactly like sending it anywhere else.
The only real catch is UPS, FedEx, and DHL Express, which need Street Addressing on the recipient’s end first. Ask for their street formatted address if you are using one of those carriers, or default to USPS when a plain PO Box is all you have.