at the intersection of the road with each recipient's carriageway or private drive allowed limited numbers of mail carriers to deliver mail to many widely scattered farms and ranches in a single day using horse-drawn wagons or later on, motor vehicles. Before the introduction of rural free delivery (RFD) by the Post Office in 1896, and in Canada in 1908, many rural residents had no access to the mail unless they collected it at a post office located many miles from their homes or hired a private express company to deliver it. For this reason, mailboxes did not become popular in rural North America until curbside RFD mail delivery by the Post Office was an established service. Even then, farmers and rural homeowners at first resisted the purchase of dedicated mailboxes, preferring to leave empty bushel baskets, tin boxes, or wooden crates at the roadside for the postman to deposit their mail. Not until 1923 did the Post Office finally mandate that every household install a mailbox or mail slot in order to receive home delivery of mail. Originally designed only for incoming mail delivery, curbside mailboxes were soon fitted with a semaphore or signal flag mounted on an attached arm to signal the postman to pickup outgoing mail. Originally, this flag was raised not only by the resident of the property to signal the postman of outgoing mail, but also by the postman to inform the recipient that incoming mail had been delivered - a convenience to all during periods of freezing or inclement weather. Since 1923, in order to promote uniformity, as well as the convenient and rapid delivery of the mail, the United States Post Office Department (later the USPS) has continued to retain authority to approve the size and other characteristics of all mail receptacles, whether mailboxes or mail slots, for use in delivery of the mails. The USPS continues to issue specifications for curbside mailbox construction for use by manufacturers. Approved mailboxes from the latter are always stamped "U.S. Mail" and "Approved by the Postmaster General". These standards have resulted in limitations on product diversity and design, though new materials, shapes, and features have appeared in recent years. 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