In Germany it's pretty tightly regulated. Cold personal mail is not a thing you get, and for unnamed mail you just put a no ads sticker on your mailbox and repeat violators are strictly punished
It’s encouraged by the US postal system, as spam mail is one of the most reliable income sources (which is necessary given how Republicans are trying to kill the public postal system).
This has led to the postal system taking legal action against startups that tried to shield people from spam.