What I've seen in quite a few flats is that at the entrance floor there's a floor plan with names, so if you know to whom it is addressed and you have the right

What I've seen in quite a few flats is that at the entrance floor there's a floor plan with names, so if you know to whom it is addressed and you have the right building you can deliver it. I've even seen more curious scenario's on islands in Greece for example where all you need to know is the person's name and the town they live in, the mailman does the rest since they make it their business to know who lives where :). People can get very creative when it comes to these things. There's a very common concept of "old lady surveillance" in the Mediterranean where the elderly sort of function like a bottomless address book if you ever need to get directions and can usually complement a police report too, since they just tend to observe everything going on in their neighbourhood. As far as mail distribution goes, I think since you can reverse the lookup to find the actual geographical location you could do that in a mail distribution centre and bundle things up for delivery, much like postcodes are used.