John Walter "Duster" Mails (October 1, 1894 – July 5, 1974) was an American pitcher in Major League Baseball for the Brooklyn Robins (1915–16), Cleveland Indians (1920–22) and St. Louis Cardinals (1925–26). Mails pitched for three pennant winning teams—the 1916 Robins, the 1920 Indians and the 1926 Cardinals. He appeared in only 11 games for the 1916 Robins, with a record of 0–1, and did not appear in the 1916 World Series, which the Robins lost. He appeared in only one game for the 1926 Cardinals, posting a record of 0–1, and did not pitch in the 1926 World Series, which the Cardinals won.