USPS Standard Cast Aluminum Mailbox Specifications

A cast aluminum mailbox is not automatically USPS approved. For curbside mail delivery, the complete mailbox design—not only its material or external dimensions—must comply with USPS-STD-7C and receive approval before a manufacturer can use markings such as “Approved By The Postmaster General” or “USPS-Approved.”

Core USPS Mailbox Requirements

Traditional and contemporary curbside mailboxes must provide enough internal capacity to accept a USPS test gauge measuring 18.5 inches long, 5 inches wide and 6 inches high. The gauge must enter and leave the mailbox easily while allowing the door to close completely.

Full-service mailboxes also require a carrier signal flag mounted on the right side when viewed from the front. The flag must remain in position when raised and operate without excessive force. Limited-service models without a flag are intended only for incoming mail and do not support outgoing-mail pickup.

Mailbox doors, hinges, catches and other moving parts should operate smoothly. The finished product must not contain sharp edges, burrs, hazardous projections or components that interfere with delivery. Powder coatings and other finishes should remain free from peeling, cracking, flaking or powdery surfaces.

Approved models must display “U.S. MAIL” and “Approved By The Postmaster General” on the carrier door. The manufacturer’s name, address, model number and production date must also be permanently identified.

Installation Requirements

USPS generally recommends positioning the bottom of the mailbox or mail-entry point 41–45 inches above the road surface. The mailbox door should be located 6–8 inches behind the curb or road edge. Mailbox posts should normally be buried no more than 24 inches. Buyers should contact the local post office before installation because placement requirements may vary by road and delivery route.

Specifications for OEM Buyers

When sourcing a custom cast aluminum mailbox, confirm:

• Internal mail capacity and door opening

• Mailbox body and post dimensions

• Flag location and operating force

• Door-latch performance

• Mounting and breakaway-post structure

• Powder-coating and corrosion protection

• Address-number and logo positions

• Permanent manufacturer markings

• Product testing and approval status

Decorative cast aluminum posts, plaques and newspaper holders must not obstruct the carrier, hide the signal flag or extend beyond the front of the closed mailbox.

Most importantly, request proof that the exact mailbox model has received PMG approval. Using cast aluminum, standard dimensions or an outdoor powder coating does not by itself make a mailbox USPS compliant.