Plus post offices in a lot of countries do tons of other stuff like fishing licenses and random stuff. This is likely part of a early sorting system which would have required rooms of electronics when created and something like a single ibm 2 and backend hardware a handful of years later.
They were also processing packages. There were several floors with conveyor belts and lifts. I agree though, that is a lot of electronics.
Plus post offices in a lot of countries do tons of other stuff like fishing licenses and random stuff. This is likely part of a early sorting system which would have required rooms of electronics when created and something like a single ibm 2 and backend hardware a handful of years later.