For some nice nitpicking, a postitoimipaikka isn't necessarily the name of the city/municipality. At least within the city of Kotka, the postitoimipaikka for the former kauppala (market town?) of Karhula was "Karhula". That was changed a few years back to "Kotka", but I have no idea whether some of these exceptions still exist.
Literally translated it or more-or-less means 'place where post is to be sent'. Meaning suburb if there is one etc. So you wouldn't say 'Helsinki' if you lived in 'Espoo' or something. But I think the OP gets the point.
I̶f I can find any way to insult someone, believe me I will.
Espoo used to be a rural county, actually Kauniainen got incorporated a a "town" way before Espoo country hicks were considered an entity. That is of course suburbs of Helsinki such as Pasila, Töölö, and Herttoniemi were "villages".... you need to find yourself a map of Helsinki in 1932... theres a !"#¤% of railways, but the "built-up-area sort of... ends.
"By the pricking of my thumbs, Something wicked this way comes."