What USPS says about your curbside mailbox.

The two numbers people ask about are 41 to 45 inches of height and 6 to 8 inches of setback. Both are real, and both come from one sentence in the USPS engineering standard for mailboxes.

Two things in that sentence get lost when it is repeated. The word is generally, not “must” — the part written as a requirement is the first sentence, which tells you to ask your local Post Office. And the height is measured to the inside floor of the box, the surface the carrier sets mail on, not to its outside underside.

The customer-facing page on usps.com simplifies that second point, and the two do not quite agree. It says to position the mailbox 41 to 45 inches from the road surface “to the bottom of the mailbox or point of mail entry”, and calls the whole list “some helpful guidelines” (usps.com, Mailbox Guidelines (retrieved September 22, 2026) — the page writes the figures with inch marks). Where the two differ we have quoted the engineering standard above, because that is the document the Postal Operations Manual points to.

The setback is measured from the front face of the curb, or the road edge where there is no curb, to the mailbox door. usps.com adds that if you have no raised curb you should ask your local postmaster.

The mailbox at the curb is yours. USPS is explicit about this, twice, in two different manuals.

The Postal Operations Manual says the same thing and adds where to check placement: “Purchase, installation, and maintenance of mail receptacles are the responsibility of the customer. Appropriate locations for installation should be verified with local Postmasters.” (POM 632.11 (retrieved September 22, 2026))

If a box stops meeting the rules, the first thing that happens is a notice, not a stopped delivery. A carrier reports it, and “the postmaster sends PS Form 4056, Your Mailbox Needs Attention, to the owners of these boxes to request that they remedy the irregularities or defects” (POM 632.53). Delivery being withdrawn is written about something else: an approach that is blocked, so the carrier cannot safely reach the box (DMM 508.3.1.4). We found nothing in any USPS document saying mail is withheld because a curbside mailbox looks worn.

These are two different things, and the second is the one everybody quotes as though it were the first. What USPS itself requires of a post is one sentence, and it contains no dimensions:

The familiar 4 by 4 and the 2-inch pipe come from the Federal Highway Administration. usps.com publishes them and attributes them in its own sentence: “The best mailbox supports are stable but bend or fall away if a car hits them. The Federal Highway Administration recommends” a 4 by 4 inch wooden support or a 2 inch diameter standard steel or aluminum pipe, avoiding “unyielding and potentially dangerous supports, like heavy metal pipes, concrete posts, and farm equipment”, and burying the post no more than 24 inches deep (usps.com, Installing the Mailbox Post (retrieved September 22, 2026) — the page writes the dimensions with inch marks).

So: a recommendation, from the highway agency, about what happens when a car hits it. There is no USPS rule that a mailbox post must break away. If someone tells you a brick pillar is against postal regulations, that is not where the objection comes from — and it is a real objection, because of what the highway guidance says and because of who owns the strip of ground the post stands in. Our guide to post materials goes into that.

The rule is shorter and looser than the version that circulates. Here it is whole, both bullets, because the difference between them is the whole point:

The “at least 1 inch high” and “contrasting color” belong to the first bullet, about a box number on a rural route. The house-number bullet gives no size, no colour and no position. We looked for one and did not find it, so this page does not state one. Legible and contrasting is good practice — it is not a USPS figure we can show you.

One more line worth knowing before anyone puts anything on a mailbox: “Any advertising on a mailbox or its support is prohibited” (DMM 508.3.2.5). A crew that offers to leave its name on your box is offering you a problem.

This one matters if anyone is repainting. The engineering standard rules five colours out for the carrier signal flag, and requires it to contrast with the box:

Red is not on the excluded list, and red on a black box is a clear contrast, which is why almost every flag in Northern Virginia is red. The standard also says the flag must sit on the right side facing the box from the front, must take no more than 2 pounds of force to retract, and must stay up once raised until the carrier puts it down (§3.6).

Read that paragraph as a warning about paint. A flag painted the same black as the box no longer contrasts, and a flag painted stiff in its hinge no longer retracts under 2 pounds. Both are easy to do by accident with a spray can.

We can tell you what we found, and what we did not. We found no USPS prohibition on repainting a mailbox in any of the four documents we read. We did find USPS asking homeowners to do it: its own Mailbox Improvement Week release lists “repainting a mailbox that may have rusted or has started to peel” among the tasks it asks people to take on (USPS newsroom, Mailbox Improvement Week (retrieved September 22, 2026)). The same usps.com page recommends an annual checkup, and its list is almost our job description: tighten loose hinges, take care of rusty or loose parts, replace missing or faded house numbers, keep the path clear.

What we did not find is a sentence addressed to homeowners saying painting is permitted. The absence of a prohibition across four documents is good evidence and it is not the same thing, so we are not going to dress it up as one.

Two things to keep off the brush, from the standard rather than from opinion:

• The flag, if you paint it a colour on the excluded list above, or thick enough that it stops moving freely.
• The markings on the carrier door. A manufactured box carries “U.S. MAIL” and “Approved By The Postmaster General” in stated letter heights (§3.7). Those sections are addressed to manufacturers, not to you, so we are not going to tell you it is a rule — but painting them out removes the one thing on the box that says what it is.

A USPS document is not the only thing with a say, and the Postal Operations Manual says so itself: “Some states have enacted laws that are more stringent and specific about the type of mailbox that may be used, the post or support that must be used to mount the mailbox, and the location of the delivery equipment. Regulations and recommendations published here might not reflect appropriate requirements for your area.” (POM 632.54)

In practice there are three layers over a mailbox in Loudoun and Fairfax counties: the postal rules above, whoever maintains the road the box stands beside, and, on most streets built in the last forty years, a community association with a recorded standard of its own. Those are separate authorities with separate paperwork, and a letter from one of them tells you nothing about the others. The guide to an association letter covers the third.

The one USPS line that resolves most arguments is the first one quoted on this page: contact your local Post Office before you install a mailbox. It takes a minute and it is the only advice on this page that USPS writes as a requirement.