Transfer Office
From the 1880s until well into the 1950s, virtually all long-distance transportation of United States Mail was performed by the railroads. Specially equipped Railway Post Office (RPO) cars were a part of most passenger trains, the cars staffed by highly trained railway postal clerks who sorted mail as the train sped along its route. The growth of this mail distribution network paralleled the expansion of the railroads, allowing mail to be exchanged between routes at junction points where two railroads crossed or shared passenger terminals.