I rarely get any mail from legitimate companies that I'm not genuinely interested in, because if I ever end up on their list because I signed up or bought something, I just click the unsubscribe link in the email, and then I stop getting them.

If you get a bunch of mail you don't want, but don't click unaubscribe, you shouldn't be surprised when they keep aending you mail.

There are few exceptions where a legit business will continue to mail you after unsubscribing.

All that said, it did take a few months of diligently clicking unsubscribe on every promotional email I got to actually clean up my inbox, but since then it's been very smooth sailing.