I remember seeing a postal ritual while watching Pennsylvania Railroad trains with my grandfather at the station in Marysville, Pennsylvania. There was a mail crane on the side of the eastbound track and a bin to receive mail pouches thrown from the RPO. This was a fascinating scene for a child and a metaphor for the high purpose of expediting communication in an industrial world. While doing research for my model railroad I came across this filmed reminiscence on the site of the National Postal Museum. Notice that the pouch thrown from the passing B & O train simply skips across the station platform.
Railway Post Office