Why на почте rather than в почте?

Question

My understanding is that на is used to describe an open space or a space with indistinct boundaries. Clearly that does not describe почта. Is there reason why на is used here or is it an isolated exception?

Answer 1

Yes, your understanding is correct, but it isn't a strict rule. There are several exceptions. Also, you can look at these exceptions from a historical perspective. Почта is a building now but many years ago it was a place where people changed horses. На фабрике, на заводе - factories and plants were open places in the past as so railway station - на вокзале.