[bombcar]

Almost every single post office has a separate zip code (usually one higher than the city/area it is sitting in).

Some individual buildings have their own zip code, or 12345 for GE, or 20252 for Smokey Bear.

[jasomill]

My post office box has its own ZIP+4.

[bombcar]

+4 is cheating! Especially for post offices with less than 10000 boxes.