High Quality Content by WIKIPEDIA articles! The Railway Mail Service (RMS) Library is a major collection of materials pertaining to en route distribution history. Incorporated in May 2003, it can assist researchers interested in Railway Mail Service, route agent, Seapost, Railway Post Office (RPO), and Highway Post Office (HPO) history. The collection has many unique, original-source documents that provide answers to questions dealing with the transportation and distribution of USA Mail between 1862 and 1977, as well as other countries during the 19th century and 20th century.