<P> After World War II, postwar suburban home construction expanded dramatically in the United States, along with mail volume . By the 1960s, many new suburban homes were considerably larger and located on larger lots, yet most still used mail slots or attached wall - mounted mailboxes . This development caused a substantial increase in distances walked by the mail carrier, slowing mail delivery while increasing labor costs . In order to reduce delivery times and increase efficiency, the Post Office began requiring all new suburban developments to install curbside mailboxes in place of door - to - door delivery, allowing mail carriers to remain in the vehicle while delivering the mail . In 1978, the USPS (successor to the Post Office) declared that every new development must have either curbside delivery or centralized mail delivery . </P> <P> In 1915, the familiar curbside Joroleman mailbox, named after its designer, Post Office employee Roy J. Joroleman, was approved by the Post Office . Joroleman, who held a degree in mechanical engineering, designed his mailbox with an unusual dome - rectangular shape, incorporating a curved, tunnel - shaped roof, latching door, and rotating semaphore flag . The Joroleman mailbox has been praised as a manifestation of American functionalist industrial design . </P> <P> Constructed of light - gauge painted sheet steel, Joroleman designed his mailbox with an arched, tunnel - shape roof, which prevented excessive accumulation of rainwater or snow while resisting deformation . The tunnel top also simplified the process of mass production by eliminating the need for precise sheet metal bends . Stamped and formed metal straps riveted to the arched opening and the mailbox door served as a door latching mechanism, while a rotating red semaphore flag mounted on a shaft attached to the side of the mailbox served to signal the approaching mailman if there was outgoing mail inside . Fitted with a crimped or braze - on rear steel panel and a false floor to keep its contents dry in inclement or humid weather, the Joroleman mailbox required only two rivets, three axle bolts, and four screws and nuts for completion . Durable and inexpensive, the popularity of the Joroleman mailbox was further enhanced by a decision not to patent the design, but to make its specifications known to all potential manufacturers for competitive sale . Adopted across the United States, it has remained the top - selling mailbox since its introduction, and was also widely used in Canada prior to that country's decision to eliminate individual curbside delivery to rural residents . </P> <P> The Joroleman mailbox was originally approved for manufacture in one size, the No. 1, which could accommodate letter mail, periodicals, newspapers, catalogs, and small parcels . After July 1, 1916, the Joroleman mailbox would be the only design approved by the Post Office for new curbside mailbox installations . In July 1929, the Post Office approved specifications for a larger Joroleman mailbox known as the No. 2 . The No. 2 mailbox, soon followed by the still - larger No. 3, could accept larger parcels and packages sent via Parcel Post; these large boxes proved particularly popular with rural mail recipients, who could order manufactured goods by mail for delivery to the farm or ranch . </P>

What is the red thing on mailboxes for