Entitled: "Ornamented mailbox. Morris-Butler House, 1204 North Park Avenue, Indianapolis, Marion County, Indiana." A letter box, letterbox, letter plate, letter hole, mail slot or mailbox is a receptacle for receiving incoming mail at a private residence or business. For the opposite purpose of collecting outgoing mail, a post box is generally used instead. Until 1916, in the United States, mail carriers knocked on the door and waited patiently for someone to answer. Efficiency experts estimated that each mailman lost over 1.5 hours each day just waiting for patrons to come to the door. To correct this problem, the Post Office Department ordered that every household must have a mail box or letter slot in order to receive mail. This requirement was phased in, starting with new delivery locations, around 1912. Slowly, homeowners and businesses began to install mail slots or attached mailboxes to receive mail when they were either not at home or unable to answer the door. The requirement was made mandatory in 1923. Photographed for Historic American Buildings Survey by Jack E. Boucher, August 13, 1970.