The relationship between the French Poste (Post Office) and the railway companies began in 1845 on the Paris-Rouen line. From then on, the number of mail wagons (or itinerants) set up on the various networks continued to increase until the Second World War. As soon as the SNCF was created in 1937, post wagons with mail sorting on board and lighters – which carried mail without sorting – were incorporated into most of the company’s fast trains. The Poste owns the rolling stock used to transport mail, but the SNCF is required to maintain the rolling stock in good condition.