The turn of the last century brought many changes affecting mail transportation and delivery. Pneumatic tubes sped mail underground. In 1913 the Post Office rolled out Parcel Post Service, allowing packages up to 50 pounds in the mail. Letters were joined by tons of packages and postmasters needed trucks to carry all that mail. The end of RPO trolley cars was in sight.
San Francisco stopped the service in 1906. New York postal officials put an end to trolley mail service in 1900, Rochester in 1909. The service ended in most of the remaining cities between 1913 and 1919. Baltimore ended the service in 1929. Trolley mail was no more.