Parts of a Mailbox – Flag, Door, Latch, Body and Post

All 7 parts on the diagram

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Start here: 4 main parts 4

Flag The flag: a red arm on a pivot on the side. Raised, it tells the mail carrier there is outgoing mail inside.
Body A metal box with a rounded "tunnel" top that sheds rain. It is big enough for letters, magazines and small parcels.
Post The post: a support that holds the box up at the curb. The Federal Highway Administration recommends a 4 by 4 inch wooden post or a 2-inch metal pipe, which bends or falls away if a car hits it.
Door The arched front end. It opens for the mail to go in and come out.

From the side: 4 1

House numbers On the box's side so the carrier can find the address. If the box is on a different street, the full street address goes on it.

The front: 3 2

Latch A catch at the top of the door that holds it shut.
Hinge The hinge, along the bottom of the door, so it drops open. Loose hinges are one of the things to check each year.

How this list was compiled: Read 2026-09-27. (1) United States Postal Service, Mailbox Guidelines, https://www.usps.com/manage/mailboxes.htm : curbside mailboxes with the Postmaster General’s approval meet USPS size and construction standards; place the box 6 to 8 inches back from the curb; put the full street address on the box if it is on a different street; the Federal Highway Administration recommends a 4 by 4 inch wooden support or a 2-inch steel or aluminum pipe, stable but able to bend or fall away if hit by a car; bury the post no more than 24 inches deep; yearly checks: tighten loose hinges on the door, replace missing or faded house numbers. (2) Wikipedia, Letter box, https://en.wikipedia.org/wiki/Letter_box : curbside mailboxes are a metal box on a support, often with a flag to signal outgoing mail; the Joroleman design (1915) has a tunnel (arched) top, a door with a latch, and a rotating red semaphore flag on a shaft on the side, raised to show outgoing mail; sizes No. 1 to No. 3. Licence: own work

The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work

How it works

These are the parts of a mailbox on a standard US curbside mailbox: first from the side on its post, then its front end with the door. Start with the 4 main parts.

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From the side

The body is a metal box with a rounded top that sheds rain. A red flag on the side is raised to tell the mail carrier there is mail to collect. House numbers on the side help the carrier find you, and the post holds the box at the curb.

The front

The door is the arched front end. A latch at the top keeps it shut, and a hinge along the bottom lets it drop open.

Raise the flag only when there is outgoing mail inside: a raised flag is how the carrier knows to stop and collect it.

Questions and answers

What is the flag on a mailbox for?

It signals the mail carrier. When the flag is raised, there is outgoing mail in the box to be picked up.

How far from the curb should a mailbox be?

The US Postal Service asks for the front of the box to be 6 to 8 inches back from the curb, so the carrier can reach it from the vehicle.

What kind of post should a mailbox have?

One that is stable but gives way if a car hits it. The Federal Highway Administration recommends a 4 by 4 inch wooden post or a 2-inch metal pipe.