The United States Postal Service sets standards for curbside mailboxes under USPS-STD-7C, and publishes separate installation guidance for placement, wall-mount mailboxes, and door slots. Requirements differ depending on which you have, and several rules commonly attributed to the USPS actually come from elsewhere.
Locking mailboxes deter theft of incoming mail. They must meet the same functional requirements as standard mailboxes. Every Mail Boss post mount mailbox model is approved under USPS-STD-7C and listed in each year's Mailbox Improvement Week Postal Bulletin, found under Epoch Design.
How USPS Classifies Curbside Mailboxes
USPS sorts curbside mailboxes into two groups. Non-locked designs come in traditional, traditional wide, and contemporary styles. Locked designs come in mail slot and wide or large-capacity formats.
Approved manufacturers are published annually in the Postal Bulletin. One point people get wrong: your local postmaster does not approve manufactured mailboxes, USPS Engineering does. Local postmaster approval applies to homemade and custom-built boxes, which still have to meet standards for flag, size, safety, strength, and construction quality.
Placement and Height
Install your mailbox 41 to 45 inches above the road surface, measured to the bottom of the box or the point of mail entry. On Mail Boss locking curbside mailboxes, that point is the lower edge of the upper delivery door, the one stamped "U.S. MAIL."
Set it back 6 to 8 inches from the front face of the curb or road edge to the mailbox door.
Your mailbox belongs on the right-hand side of the road in the direction the carrier travels, and on new rural or contract routes this is typically required. Carriers must be able to deliver mail without leaving the vehicle, which also means keeping the approach clear of parked cars, trash cans, and snow.
Address numbers can go on the side of a single mailbox, and should go on the door if boxes are grouped side by side. Use a contrasting color, with characters no less than 1 inch tall. If your mailbox sits on a street other than the one you live on, put the full street address on it.
Names are not required. USPS says putting your name on the mailbox is optional and not recommended. A surname on a mailbox tells anyone walking by exactly who lives there, which is useful information to anyone planning to steal your mail.
Mailbox Posts Are Not a USPS Requirement
The USPS does not regulate mailbox supports except as they affect carrier safety and delivery efficiency. You own your post, and you are responsible for keeping it sound.
The familiar specifications come from the Federal Highway Administration. The FHWA has determined that a 4 by 4 inch wooden support, or a 2 inch diameter steel or aluminum pipe, buried no more than 24 inches, should break away safely if a vehicle strikes it. FHWA also says to attach the mailbox to the post securely enough that the two do not separate on impact.
Mail Boss posts are hollow steel, which allows them to be installed directly in the ground or sleeved over a wood post or depth extender depending on your site. We do not test our posts to FHWA breakaway criteria and make no representations about their performance in a vehicle impact. Check your local codes, since some jurisdictions specify post construction directly.
One practical note: because the mailbox mounts to the post rather than forming part of it, a damaged post can usually be replaced without replacing the mailbox, and a damaged mailbox without replacing the post. That is also why we sell posts separately and keep replacement parts in stock. A mailbox backed by a lifetime warranty is worth remounting.
In areas where snowplows are a recurring problem, USPS suggests a semi-arch or extended-arm support, which lets a plow sweep near or under the box without taking out the post. While we don't make an off-the-shelf option, we have seen many creative solutions to this problem.
For all post mount mailbox installations, local codes, state law, and HOA rules may all still apply. In practice, those are the rules that often get enforced. Check with your city or county before your mailbox install, and with your HOA if you have one, since restrictions on post material and mailbox style are common.
Locking Mailboxes
The rule people most often misunderstand is that you cannot add a lock to a standard, non-locking mailbox. USPS prohibits locks, hasps, and inserts on any design approved as non-locking, including anything that requires the carrier to use a key or that narrows the interior opening once the door is open. There is no local postmaster exception. The takeaway is not that locks are forbidden, but that the mailbox has to be designed to lock from the start and approved by USPS Engineering on that basis.
A purpose-built locking mailbox functions simply. Mail goes through a slot or delivery door on the upper front of the box and drops into a lower, secure area that only you can open. That incoming mail slot must be, at minimum, 1.75 inches high by 10 inches wide, positioned facing the street, clearly visible and directly accessible. USPS Engineering ensures and verifies that standard mail actually fits and comes back out easily, using a Priority Mail envelope and a Priority Mail box measuring 8.625 by 5.375 by 1.625 inches.
USPS is also explicit that carriers are not responsible for opening locked mailboxes, accepting keys for that purpose, or locking a mailbox after delivery. Any locking design that depended on those things would not be approved.
Package and Large-Capacity Mailboxes
USPS encourages larger curbside mailboxes that hold packages alongside regular mail, and markets them as Next Generation Mailboxes. The target size is roughly 13.63 inches wide, 7.75 inches tall at the sides, 12 inches tall at the center, and 16.5 inches deep, though USPS notes that these figures are approximate and vary by manufacturer. The Orca Non-Locking Mailbox is USPS approved and sized to the Next Generation Mailbox dimensions.
A larger box means packages arrive with your mail instead of sitting on the porch, and a closed box keeps them out of sight. But a Next Generation Mailbox is still unlocked, and concealment is not the same as security. Anyone who opens the door has everything inside.
USPS also encourages, without requiring, grouping mailboxes where several are located near a crossroads or turnout. Grouped installations are served in one stop, and shared posts and spreader bars make that straightforward.
Wall Mount Mailboxes
Wall mount mailboxes serve addresses on foot delivery routes and are a practical choice for residents with limited mobility.
If you currently receive curbside delivery, you cannot simply move your mailbox to the house. You need your local postmaster's permission first, because it changes how the route is served. Wall mount mailboxes are not required to carry the Postmaster General seal, so you have more latitude in size and style. Choose one that holds a normal day of mail including letters, postcards, and catalogs, and mount it near your main entrance where the carrier can easily see it.
The 41 to 45 inch height and 6 to 8 inch setback figures do not apply here. Those exist so a carrier can reach a mailbox from a vehicle, and neither matters on a walking route. As a general guideline, we find a height of 55 to 65 inches comfortable for walk-up delivery and easy access.
Newspaper Receptacles
A newspaper receptacle may be attached to your mailbox post. It cannot interfere with mail delivery, block the view of the flag, extend past the front of the closed mailbox, or create a hazard for the carrier.
Door Mail Slots
Homes with door delivery through a slot follow their own standards. The opening must be at least 1 1/2 by 7 inches, with the bottom of the slot at least 30 inches above the floor. Horizontal slots hinge at the top, and vertical slots hinge on the opposite side from the door's hinges.
Maintenance
USPS asks customers to paint mailboxes and posts and keep them rust-free, and recommends an annual checkup. Check for loose hardware and components, touch up any dings or scratches in the finish, replace faded or missing address numbers and flags, and keep the path to your mailbox clear.
Pro tip: if your lock starts sticking, skip standard WD-40 Multi-Use Product. It attracts dirt and dust, gumming up the mechanism over time. Reach for a dry lubricant instead. Tri-Flow, WD-40 Specialist Dry Lube with PTFE, and Hexkote all work well on our locks.
Questions About Your Installation
Regulations get interpreted differently from route to route, and your local Post Office is always the final word on mailbox placement. If you are working out which mailbox suits your situation, or you have a question this guide did not answer, comment below or reach out to us. Our team is happy to help.
We design and engineer Mail Boss mailboxes in Arlington, Washington, and every order, warranty claim, and question is handled by our team here.
Originally published February 6, 2018 · Last Updated July 2026