USPS mailbox requirements come down to five things: a curbside box must be an approved model (it carries "Approved by the Postmaster General" on the door) or a custom box your postmaster accepts; it sits 41 to 45 inches above the road and 6 to 8 inches back from the curb; it shows your house number in 1-inch characters; it rides on a post that gives way if hit; and the carrier can reach it without leaving the vehicle.
That is the short version. Below is every rule a homeowner is likely to run into, where it comes from, and what it means when you shop. If you already know you need a compliant curbside box, our USPS approved mailboxes collection only lists models built to the current curbside standard.
USPS mailbox requirements at a glance
| Requirement | What USPS says | Where it comes from |
|---|---|---|
| Approval | New or replacement curbside boxes must be approved models; custom-built boxes need your local postmaster's OK | DMM 508.3.2, POM 632.5, USPS-STD-7C |
| Height | Generally 41 to 45 inches from the road surface to the bottom of the box or point of mail entry | usps.com mailbox guidelines, USPS-STD-7C |
| Setback | Generally 6 to 8 inches from the front face of the curb or road edge to the mailbox door | usps.com, USPS-STD-7C |
| Location | Served safely from the vehicle; on the right-hand side of the road on new rural routes | DMM 508.3.2.6 |
| Numbers | Contrasting color, neat characters at least 1 inch high, visible to the approaching carrier | DMM 508.3.2.7 |
| Post | Neat and strong; a 4x4 wood post or 2-inch steel or aluminum pipe, buried no more than 24 inches | DMM 508.3.2.4, usps.com |
| Flag | Mounted on the right side; any color except shades of green, brown, white, yellow or blue | USPS-STD-7C |
| Advertising | Not allowed on the box or its support | DMM 508.3.2.5 |
Who sets the mailbox rules
Three USPS documents do most of the work, and your state and town can add to them.
- Domestic Mail Manual (DMM) 508 is the customer-facing rulebook. Section 3.2 covers curbside mailboxes: approval, posts, location, numbers and advertising. Read DMM 508 on Postal Explorer.
- Postal Operations Manual (POM) 632.5 is what postmasters and carriers follow for the construction and placement of mailboxes and supports. POM 632.53 covers how they notify you if your box is "nonconforming."
- USPS-STD-7C is the engineering standard manufacturers must pass to put the approval wording on a curbside box. The full standard is published by USPS.
On top of that, state highway departments and towns often regulate posts and placement in the road right-of-way, and HOAs may dictate style. USPS itself notes that some states are stricter than postal rules. Your local postmaster has the final say on where the box goes.
What makes a mailbox USPS approved
A curbside mailbox is "USPS approved" when its manufacturer has submitted the design for testing under USPS-STD-7C and USPS has accepted it. Approved boxes must carry "U.S. MAIL" and "Approved by the Postmaster General" on the carrier's door, plus the maker's name, model and date of manufacture on a panel.
The standard tests much more than looks. Boxes go through capacity checks with a test gauge, 7,500 door opening and closing cycles, a rain test, salt spray, abrasion (metal boxes) and a cold-weather impact test. Locked large-capacity designs also pass a security test performed by USPS.
The five approved design types
| Code | Design | What it means |
|---|---|---|
| T | Traditional | The classic tunnel (dome-top) shape |
| C | Contemporary | Any other shape with the same minimum capacity |
| LC | Large Capacity | Must swallow a larger test gauge (16 x 13 x 7 inches), sized for small parcels |
| LMS | Locked, mail slot | Locking box with an incoming slot at least 1.75 inches high by 10 inches wide |
| LLC | Locked, large capacity | Locking box that meets the large gauge and passes USPS security testing |
Each type can be "full service" (it has a carrier signal flag, so the carrier also collects outgoing mail) or "limited service" (no flag, delivery only). For the actual sizes and what fits inside each, see our guide to mailbox sizes and dimensions.
How to check whether a specific model is approved
USPS publishes the approved manufacturer list in the Postal Bulletin each spring for Mailbox Improvement Week. The May 2026 list (Postal Bulletin 22702) includes, among many others, Mail Boss Mail Manager and Package Master models from Epoch Design, the Whitehall Capitol and Balmoral, and the Salsbury 4325, 4350, 4375 and 4850 series. Look for the approval wording on the door, or ask us before you order.
For example, the Mail Boss Mail Manager is a locking steel box approved for curbside delivery, and the Whitehall Capitol Mailbox is a cast aluminum non-locking box listed as a contemporary design.
Can I build my own mailbox?
Yes, with the postmaster's blessing. DMM 508.3.2.2 lets the local postmaster approve a customer-built curbside box if it generally meets the same standards as approved boxes for flag, size, strength and construction. Approval is case by case. Show the postmaster your plans before you build, not after.
Locking mailbox rules
Locking curbside boxes are allowed, and USPS lists "wide or large-capacity" locked designs as a preferred type. The catch: carriers do not carry your key, so everything must go in through the slot. DMM 508.3.2.3 says a locked box must have a slot big enough for your normal daily mail, and STD-7C sets the minimum slot at 1.75 by 10 inches. If parcels are a big part of your mail, a large-capacity locking box saves trips to the post office. Check the slot and capacity specs before you buy.
One thing you cannot do: add a padlock or aftermarket lock to a regular non-locking box. STD-7C prohibits locks on non-locked designs, and a box the carrier cannot open will not get mail. Buy a box that was approved as a locking design instead; our locking mailboxes collection is the place to start.
Mailbox height and placement rules
USPS mailbox guidelines ask for 41 to 45 inches from the road surface to the bottom of the box or the point of mail entry, and 6 to 8 inches from the front face of the curb (or road edge) back to the mailbox door. If you have no raised curb, USPS says to ask your local postmaster.
Location matters as much as height. DMM 508.3.2.6 requires that the carrier can serve the box safely without leaving the vehicle. On new rural routes all boxes go on the right-hand side of the road in the carrier's direction of travel, and elsewhere where traffic makes left-side delivery unsafe. You also have to keep the approach clear: parked cars, trash cans and snow banks can get delivery suspended.
Measuring, slopes, ditches, rural roads and shared driveways are covered step by step in how high should a mailbox be.
Mailbox post requirements
USPS does not approve posts, but it does say what a safe one looks like. The post must be "neat and of adequate strength and size." The best supports are stable in normal use but bend or fall away if a car hits them.
- Use a 4x4 wooden post or a 2-inch diameter standard steel or aluminum pipe (Federal Highway Administration guidance quoted by USPS).
- Bury it no more than 24 inches deep.
- Avoid heavy metal pipes, concrete posts, and novelties such as concrete-filled milk cans.
- Attach the box securely so it does not separate from the post on impact.
- Nothing on the post may stick out past the front of the mailbox.
Where snowplows are a problem, USPS suggests a semi-arch or extended-arm support so the plow can clear under the box. Call 811 before you dig.
House number requirements
Your mailbox must show your house number (or rural box number) in a contrasting color, in neat characters at least 1 inch high, on the side the carrier sees as they approach. On grouped boxes, the number goes on the door. If the box is on a different street from your house, put the street name and number on it. Adding your name is optional, and USPS does not recommend it. Full detail, plus how 911 address rules differ, is in our guide to mailbox and house number requirements.
Flag rules
On approved boxes the carrier signal flag sits on the right side as you face the box. It can be any color except shades of green, brown, white, yellow or blue, and it must contrast with the box. USPS-STD-7C names fluorescent orange as the preferred color, which is why most flags are red or orange.
Wall-mounted mailboxes and door slots
The curbside standard does not apply to boxes at your door. According to USPS, wall-mounted mailboxes do not need the PMG seal, but you need your local postmaster's permission to switch from curbside to a wall box. Place it near the main entrance where the carrier can see it. Browse wall mount mailboxes if you have door delivery.
Door slots have their own rules: a clear opening of at least 1-1/2 by 7 inches, the bottom of the slot at least 30 inches above the floor, a horizontal flap hinged at the top (vertical flaps hinged on the side opposite the door hinges).
New homes and subdivisions
If you are building, you may not get a curbside box at all. USPS says centralized delivery is its preferred method for all new addresses, and its 2026 Mailbox Improvement Week bulletin names cluster box units (CBUs) as the required outdoor pedestal option for new single-family and townhome developments. Talk to the local Post Office's growth or delivery manager early. See our cluster mailbox (CBU) buying guide for HOAs and developers.
Other rules people miss
- No advertising on the mailbox or its post.
- Newspaper holders may be attached to the mailbox post, not the box: DMM 508.3.2.11 says the holder must not touch the mailbox or use it for support, block the flag or delivery, stick out past the front of the closed box, or show anything but the publication's name. Newspapers do not go inside the mailbox.
- Sharing a box: up to five families can share one curbside receptacle with a signed agreement filed with the postmaster.
- Nonconforming boxes: if your box does not meet the rules, the postmaster sends a notice (PS Form 4056, "Your Mailbox Needs Attention") explaining what to fix.
- Tampering is a federal crime: damaging or breaking into a mailbox can bring fines of up to $250,000 and up to three years in prison (18 U.S.C. 1705).
A quick checklist before you buy
- Confirm with your Post Office that you get curbside delivery, and ask if anything local applies.
- Check HOA covenants and any town or state rules for posts in the right-of-way.
- Pick an approved model sized for your mail and packages.
- Choose a post that gives way on impact, and plan for 41 to 45 inches and 6 to 8 inches setback.
- Add 1-inch (or larger) contrasting house numbers on the side the carrier approaches from.
- Call 811 before digging.
Shop compliant mailboxes
Start with our USPS-approved mailboxes or the full range of residential mailboxes. Not sure a model will pass with your postmaster? Contact us and we will check it for you.
Frequently asked questions
What are the USPS requirements for a mailbox?
An approved model (or a custom box your postmaster accepts), 41 to 45 inches high, 6 to 8 inches back from the curb, reachable from the vehicle, 1-inch contrasting house numbers, and a post that gives way if hit.
Does my mailbox have to be USPS approved?
New and replacement curbside mailboxes must be approved models, or a custom-built box the local postmaster approves. Wall-mounted boxes at the house do not need the PMG seal, but switching to one needs postmaster permission.
What is USPS-STD-7C?
It is the USPS engineering standard for curbside mailboxes, dated September 2015. Manufacturers must pass its capacity, durability, weather and (for locking boxes) security tests to label a box "Approved by the Postmaster General."
Are locking mailboxes allowed by USPS?
Yes. Locked designs are approved under USPS-STD-7C. The slot must be at least 1.75 by 10 inches and big enough for your normal daily mail, because the carrier will not unlock the box.
Can I put my mailbox on a brick or concrete column?
USPS warns against unyielding supports like concrete posts, and some states restrict them near the road. Ask your postmaster and check local rules first, and consider a breakaway post in high-traffic spots.
Who do I ask about mailbox placement?
Your local Post Office. USPS asks customers to contact them before installing or replacing a box or post, since road conditions vary and the postmaster has the final say.
******It is always recommended to contact your local postmaster prior to installation. While most of our mailboxes are USPS-approved your local postmaster may have specific preferences in terms of mailbox types and installation location******