The United States Postal Service (USPS) sets the rules for mailboxes in the country. It doesn't distinguish between rural and urban areas, but it does have standards that all mailboxes must meet. USPS customers are responsible for purchasing, installing, maintaining and replacing their mailboxes according to the Residential Mailbox Standards.
The U.S. Postal Service doesn't sell mailboxes, but it does require that mailboxes are approved by the USPS. Many department stores, home improvement stores and online retailers sell mailboxes that carry the postal service's approval. If you build your own or purchase a custom design that hasn't been approved, you can take it to your local postmaster to make sure it meets USPS standards.
When you install the mailbox, the bottom of the box should be 41 to 45 inches above the road surface unless the road or curb doesn't allow it. If that's the case, check with your postmaster before changing the location of the box. Locate mailboxes on the right-hand side where the carrier drives. Locate mailboxes on the opposite side of the road only if there is no traffic danger and no laws would be broken if the carrier drives on the left side of the road. Set the mailbox door back 6 to 8 inches from the curb or road edge.
Postal recipients are responsible for installing posts and maintaining them. The USPS says to keep neat, and they must be strong enough to support the mailbox. Ideally, the USPS says to assemble posts so they bend or fall away if they get struck by a vehicle. The Postal Service also reminds that postal recipients are responsible for keeping a clear path to the mailbox so carriers can deliver mail "safely and efficiently."
The USPS says to write the name on your box in letters at least one inch high. If your box has a lock, the USPS must approve it. You may not put any advertising on the box or its support post. Attach a newspaper delivery box to the mailbox post as long as it doesn't interfere with mail delivery or extend beyond the front of the mailbox.