When railway mail service began, mostly letter mail was sorted on the cars, which were not equipped to distribute other kinds of mail. By about 1869, other mail, except packages, was sorted as well.

In 1930, more than 10,000 trains were used to move the mail into every city, town, and village in the United States. Following passage of the Transportation Act of 1958, mail-carrying passenger trains declined rapidly. By 1965, only 190 trains carried mail; by 1970, the railroads carried virtually no First-Class Mail.

On April 30, 1971, the Post Office Department terminated seven of the eight remaining routes. The lone, surviving railway post office ran between New York and Washington, D.C., and made its last run on June 30, 1977.