Although now a familiar sight at busy intersections in every city, mailboxes were not used until the 1850s, after the introduction of postage stamps. Before 1847, everyone had to take his or her letters to the post office, pay the postage, and have the postmaster mark each item “paid.” Once people could keep stamps at home and mail letters at their leisure, the Post Office Department began placing mail collection boxes on the sidewalks around the city for convenience. As an alternative to the official Post Office Department, private mail carriers offered courier services and had drop boxes in large cities.
Residential mailboxes appeared later, as mail services expanded. In 1863, with the creation of Free City Delivery, letter carriers began delivering mail to home addresses. In 1923 the Post Office Department mandated that all residents provide a box or slot in order to receive their mail. A number of businesses sprang up to sell mailboxes of all shapes, sizes, and degrees of usefulness. Finally, the Post Office Department issued a list of standards each mailbox had to meet. Designs that meet those criteria are still labeled “Approved by the Postmaster General.”
Allison Marsh, National Postal Museum