and got my mail cut by a lot. This is not a government thing, and it doesn't affect charities. But it does help.
When I get unwanted mail now, I go to the company's web site and send an e-mail asking to be taken off. It usually works.
Don't send the mail back. The post office will just throw it away, because it's just bulk mail with something wrong with it. You will be making life harder for the letter carrier and clerks in your own neighborhood. From what I have seen, those people don't need any more hassles.
I take my junk mail down to a church, which recycles it to help feed the hungry.