Architectural Mailboxes Pewter Galvanized Steel Post Mounted Mailbox 18.3 L x 12 H x 14 W in.The Centennial Mailbox by Architectural Mailboxes is the first design to receive United States Postal Service approval against the new USPS Standard 7C regulation, released in late 2015. Named Centennial, it represents the next generation of mailbox size, since the last traditional size was introduced over 100 years ago in 1915. Meeting the needs of todays consumer, its ample mailbox compartment is designed to receive not only mail and magazines but