[kolinko]

If you live in a house you can generate tens of thousands of addresses that will be delivered to you without much problem.

You just begin inventing apt. numbers - having up to a thousand apts in a building is not suspicious. And once you cross a thousand, you can invent new buildings by strapping letter names to your home number, so that gives you a-z * 1000 = 24000 unique addresses you can generate easily. Without much hassle you could extend that to a million.

Requiring a unique mailing address is just as pointless as a unique email.

[apple4ever]

But we have databases of addresses and we can tell if it actually has 1000 apartments.

[ill13]

Who's updating those db's when I turn my single family in to a tri-plex , then convert it to an 10 unit apartment complex?

The answer is "no one".

[Strom]

That depends on where you live. In my country the government keeps an up-to-date db. Everything else in the country depends on and queries that db too, so it's not isolated.