In 1830, General Post Office and the Liverpool and Manchester Railway reached an agreement that meant mail was carried by train between Liverpool and Manchester. This led to the passing of the Railways (Conveyance of Mails) Act in 1838 which required railway companies to carry mail by ordinary or special Travelling Post Office (TPO) trains.
Following its introduction, the process of exchanging postbags at stations improved greatly in order to maintain the speed. By 1853, there were 42 mail drop sites in operation.
In 1963, there were 49 mail trains in operation, with one to five TPOs attached to passenger trains. Complete TPO trains ran between London and Aberdeen and Penzance. The use of railways for transporting mail drastically declined towards the end of the 20th century and the last TPO service ran on 9 January 2004.