This article is centered on the job of a mail carrier, a job at the bottom of the ladder in the French postal system. It examines the careers of mailmen in France from 1939 to 1974, a time of social mobility. The institutional organization of the postal service at that time offered many promotion opportunities. Working as a mail carrier was supposed to be the first stage up in the postal hierarchy. Yet, looking closely at the nature and frequency of promotions as well as investigating actual careers, make it clear that the main careers consisted in remaining a mail carrier until retirement. Far from being only a stage, working as a mail carrier was a long lasting occupation. Indeed, during the long post World War II economic expansion, postal services were a means of upward social mobility to the middle class. But the point of this article is to show that it has also contributed to empowering the working classes as many careers remained stuck at the same low level in the hierarchy.