Nobody else may use your mailbox
The rule cuts both ways. A private courier, a neighbour or a leaflet distributor putting anything in or on your box is outside what the Domestic Mail Manual permits, whatever the intention behind it.
Mailbox rules
Can I put a package in my mailbox?
For something you are sending with a printed label on it, yes, provided it fits without forcing the door. With stamps as the postage it is almost always no, because anything over half an inch thick has to go to a retail counter.
DMM 508 quotedHalf-inch clause explainedFour boxes tested
Printed postage changes the answer
The restriction USPS wrote applies to stamped items. A label bought and printed at home is not covered by it.
The rule, in the words USPS uses
Two different questions hide inside this one, and they have opposite answers. Sending is usually fine. Anybody else putting things in a mailbox is not.
- Mailboxes are for postage-paid mail and nothing else. The Domestic Mail Manual states that the receptacles described in 3.1.1 may be used only for matter bearing postage, and that no part of a mail receptacle may be used to deliver any matter not bearing postage, including items or matter placed upon, supported by, attached to, hung from, or inserted into a mail receptacle (per pe.usps.com, DMM 508.3.1.3, checked 2026-07-28). That covers flyers, neighbours dropping off borrowed things, and private couriers.
- Outgoing is a listed option. USPS names putting it in your mailbox for carrier pickup as one of the ways to send a package once the label is on it (per usps.com, checked 2026-07-28).
- Stamped mail hits a wall early. Items bearing only postage stamps as postage payment that weigh more than 10 ounces, or measure more than half an inch in thickness, must be taken to an employee at the retail counter of a Post Office (per pe.usps.com, checked 2026-07-28). Read the thickness clause twice: a light box is still a box, and almost every box is thicker than half an inch.
- The consequence is spelled out. If a stamped package breaks those limits and goes in the mailbox, the carrier leaves it there, and if it goes into a collection box it comes back to you (per usps.com, checked 2026-07-28).
How the rule lands on four real boxes
The thickness clause is what decides most of these, not the weight. Same four parcels, priced on one lane, with the published rule applied to each.
| Packed box | Weight | Label price | If stamps paid for it | With a printed label |
|---|---|---|---|---|
| 9 x 6 x 3 in | 8 oz | $8.86 | Counter only, over half an inch thick | Mailbox handoff is allowed |
| 10 x 8 x 4 in | 1 lb | $9.91 | Counter only, thickness and weight | Mailbox handoff is allowed |
| 12 x 9 x 4 in | 2 lb | $8.48 | Counter only, thickness and weight | Mailbox handoff is allowed |
| 12 x 10 x 6 in | 4 lb | $8.48 | Counter only, thickness and weight | Mailbox handoff is allowed |
Not one of those four boxes could go out with stamps on it. Every one of them can go out with a printed label, because the restriction USPS wrote applies to items bearing only postage stamps as postage payment. Printing at home is not a convenience here, it is the thing that keeps the mailbox route open.
Practical limits nobody publishes
Beyond the written rule there is physics and there is the carrier's judgement, and both can send your parcel back inside.
- It has to fit without forcing anything. A box wedged into the opening, or one propping the door open in the rain, is a box a carrier can reasonably refuse.
- Leaving the flag up is the signal. Curbside boxes have one for a reason, and a parcel sitting inside an unflagged box on a day with no incoming mail can simply be missed.
- The label has to survive the weather. Tape it flat across its whole face on the widest side; our guide on where to put a shipping label covers placement properly.
- Anything that will not fit belongs in a pickup request or at a counter. USPS will collect prepaid parcels from your door at no charge, which removes the whole problem, and the rules for that sit on our USPS package pickup guide.
Short version for anyone in a hurry. Buy the label here, print it, tape it across the widest face, then either leave the parcel in the box with the flag up or book the carrier to take it from the step.
Thickness beats weight in this rule
People remember the 10 ounce number and forget the half inch. In practice the thickness clause is the one that catches ordinary parcels, because a box tall enough to hold anything clears half an inch instantly.
A refused parcel does not vanish
A stamped package over the limits is left in the box or returned from a collection box with a note explaining why. Annoying, not catastrophic, and entirely avoidable by printing the postage.
Mailbox questions
Can I leave an outgoing package in my mailbox?
Yes, if it has postage on it and fits without jamming the door. USPS lists putting it in your mailbox for carrier pickup as one of the ways to send a package once the label is attached.
Why did my carrier leave my package in the mailbox?
Almost always because it was paid with stamps and broke a published limit. USPS requires items bearing only postage stamps that weigh more than 10 ounces, or measure more than half an inch thick, to be handed to an employee at a retail counter instead.
Can UPS or FedEx put a package in my mailbox?
No. The Domestic Mail Manual states that a mail receptacle may be used only for matter bearing postage, and that no part of it may be used to deliver anything without postage on it. Private carriers leave parcels at the door instead.
Is a printed shipping label treated the same as stamps?
No, and that is the useful part. The thickness and weight restriction is written for items bearing only postage stamps as postage payment, so a label you bought and printed keeps the mailbox and collection box routes open.