26th Base Post Office, Munich, 1957
(Source: Paul Zale)
This photo shows the rail spur on the opposite side of the building. The rail car came right up next to the building. The mail sacks were unloaded directly into the building by unit personnel and German nationals. (Those rail cars were reminiscent of the cars that carried people in the holocaust.) I am not certain, but I believe that the outgoing mail was loaded into those same cars for shipment to the USA via Bremerhaven.