USPS mailbox rules cover four things a homeowner needs to get right: the mailbox itself must carry the Postmaster General’s Seal of Approval, it has to sit 41 to 45 inches above the road with its door set 6 to 8 inches back from the curb, the support has to break away on impact, and the local postmaster has to sign off before you start using it.1United States Postal Service. Mailbox Installation Missing any of these can get delivery suspended until you fix it, at your own cost.
Approved Mailbox Types and Sizes
Any curbside mailbox you buy should carry the Postmaster General’s (PMG) Seal of Approval, which certifies the manufacturer tested the design against USPS standards.1United States Postal Service. Mailbox Installation A custom or homemade box has to meet the same standards, laid out in the technical specification USPS-STD-7C.2Federal Register. Standards Governing the Design of Curbside Mailboxes
Approved mailboxes are typically galvanized steel, aluminum, or heavy-duty plastic. A standard curbside box runs roughly 18.5 to 23 inches long, 6.25 to 11 inches wide, and 6 to 15 inches tall.
You don’t need extra approval to decorate an approved mailbox. Ornamental art and attachments are allowed as long as they don’t interfere with delivery or create a hazard, but spring-loaded designs without proper restraints are prohibited.2Federal Register. Standards Governing the Design of Curbside Mailboxes If a creative design is borderline, call your local post office before you install it.
Height and Setback From the Road
Two measurements matter most. The bottom of the interior, where the carrier drops mail, must sit between 41 and 45 inches above the road surface.3United States Postal Service. USPS-STD-7C: Mailboxes, City Delivery For a locked box with a mail slot, use the lowest edge of the slot. This height lets the carrier reach the box without leaving the vehicle.
The front face of the door must be set back 6 to 8 inches from the curb face or road edge.3United States Postal Service. USPS-STD-7C: Mailboxes, City Delivery Close enough for the carrier to reach, far enough to stay clear of traffic and snowplow overhang.
Post and Support Rules
The support has to give way when a vehicle hits it. Heavy metal posts, concrete pillars, and improvised anchors like concrete-filled milk cans are all called out as dangerous installations.4United States Postal Service. Mailbox Supports
The Federal Highway Administration sets the widely followed limits: a wooden post no larger than 4 inches by 4 inches, or a steel or aluminum pipe no larger than 2 inches in diameter, buried no deeper than 24 inches.4United States Postal Service. Mailbox Supports Supports built to those specs break away safely on impact. USPS itself does not regulate posts beyond carrier safety and delivery efficiency, but these FHWA numbers are what postal officials and local authorities expect.
A small amount of concrete around the base for stability is fine. A large concrete footing is not, because it defeats the breakaway design.
Address Numbers and the Signal Flag
Every curbside mailbox needs a clear address. Your house or box number has to be at least one inch tall, in a contrasting color, placed on the side visible to the carrier’s approach or on the door when boxes are grouped.5United States Postal Service. Requirements for City Delivery Mail Receptacles Use materials that won’t fade or peel. Carriers who can’t identify a box may send the mail back to the sender.
The outgoing mail signal flag can be any color except green, brown, white, yellow, or blue, and it must contrast with the mailbox itself. Fluorescent orange is the preferred color.6United States Postal Service. USPS Standard Mailboxes, Curbside In cluster box units, every individual compartment must be labeled with its apartment or suite number.
Locking Mailboxes
A locking mailbox with a mail slot has to give the carrier a slot at least 1.75 inches tall by 10 inches wide.3United States Postal Service. USPS-STD-7C: Mailboxes, City Delivery If the slot has a protective flap, it must swing inward so the carrier can insert mail horizontally.
Carriers will not open locked mailboxes, accept keys, or lock the box after delivery.3United States Postal Service. USPS-STD-7C: Mailboxes, City Delivery Adding an aftermarket lock or insert to a standard mailbox that forces the carrier to use a key or shrinks the interior opening is prohibited, and no local postmaster can waive that. If you want a locking box, buy one built as a locking unit.
Wall-Mounted Mailboxes
If you want a wall-mounted box on your house or porch instead of a curbside box, get permission from your local postmaster first.1United States Postal Service. Mailbox Installation Switching without approval can suspend delivery until you restore the previous setup. The postmaster considers whether the new spot fits the carrier’s route and how much walking time it adds.
Wall-mounted boxes don’t share the strict curbside height numbers, but they have to be easy for the carrier to reach from a sidewalk or porch, big enough to hold a typical day’s mail without cramming, and clear of obstructions. You are responsible for keeping the path clear of snow, ice, and overgrown landscaping.
New Construction and Cluster Boxes
If you’re building or buying in a new development, don’t count on a curbside box. Centralized delivery is the default for all new residential and commercial construction, meaning cluster box units are what builders are expected to plan for. Existing homes with curbside or door delivery keep what they have. The delivery mode for a new address is fixed when the address is first ready to receive mail.7United States Postal Service. Postal 101 – Mode of Delivery
When something breaks on a cluster box, who fixes it depends on ownership. USPS-owned units are handled by the local post office. Privately owned cluster boxes, common in condo associations and apartment complexes, are the responsibility of the property manager or HOA, including keys and locks.8United States Postal Service. Mailboxes – The Basics
What Can and Can’t Go in a Mailbox
Your mailbox is yours, but its use is regulated by federal law. Nobody, including the owner, may place anything in a mail receptacle that doesn’t bear postage.9United States Postal Service. Restrictions for Attaching Flyers, Posters, Etc. to a Mailbox That covers items placed upon, attached to, hung from, or inserted into the box. Unstamped flyers, restaurant menus, and business cards inside a mailbox are technically subject to the same postage as if they had been mailed.
The same rule covers USPS collection boxes, the blue drop boxes. No flyers, no advertisements, no missing-pet signs.9United States Postal Service. Restrictions for Attaching Flyers, Posters, Etc. to a Mailbox Door mail slots built into a front door are not regulated by USPS, so local distributors can use those.
Newspaper Boxes
A newspaper delivery box can share your mailbox post if it meets a specific set of conditions:5United States Postal Service. Requirements for City Delivery Mail Receptacles
- It cannot touch the mailbox or use any part of the mailbox for support.
- It cannot interfere with mail delivery, block the signal flag, or create a hazard for the carrier.
- It cannot extend beyond the front of the mailbox when the mailbox door is closed.
- It cannot display advertising beyond the publication’s title.
Federal Penalties for Damage and Theft
Mailboxes carry serious federal protection. Deliberately damaging, tearing down, or destroying a mailbox, or breaking one open to tamper with the mail inside, is a federal crime punishable by up to three years in prison, a fine, or both.10Office of the Law Revision Counsel. 18 U.S.C. 1705 – Destruction of Letter Boxes or Mail That applies to your neighbor’s curbside box and to USPS collection boxes.
Stealing mail is worse. Taking mail from any receptacle before the intended recipient has it is punishable by up to five years in federal prison, a fine, or both.11Office of the Law Revision Counsel. 18 U.S.C. 1708 – Theft or Receipt of Stolen Mail Matter These are federal charges investigated by the U.S. Postal Inspection Service. Vandalism and suspected theft should be reported to the Postal Inspectors, not just local police.
Installing the Mailbox the Right Way
Call 811 before you dig. The national “Call Before You Dig” service connects you with local utility companies that will mark buried gas, electric, water, and cable lines at no charge. Some lines sit just inches below the surface. Most states require a few business days’ notice.
Dig the post hole no deeper than 24 inches so the support stays breakaway-compliant. Set the box at 41 to 45 inches high with the door 6 to 8 inches back from the curb, level everything, and only then check in with your local post office. USPS requires customers to confirm placement with the local office before installing.3United States Postal Service. USPS-STD-7C: Mailboxes, City Delivery If you’re relocating an existing box, this matters even more, because the carrier’s route may need to shift. Getting the postmaster’s sign-off first is what keeps you from having to tear it all out and start again.