I remember when the CAN-SPAM act was in Congress. All of us who were following the issue looked at it and said, "this just legitimizes spam, puts a nice picket fence around it, and make sure that any company that wants to spam you knows exactly where the boundaries are so they can do so with impunity". As we expected, it didn't reduce spam at all, but now we have and industry and entire companies dedicated to mass unsolicited email. But they aren't breaking any laws.
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.
