If I'm not clear, let me describe it this way.

If you are a customer of a company or subscribing to something, you have already given them permission to mail to you. You will continue to get mail from them.

If there are Direct Mail advertisers (junk mail you have not asked for) who mail stuff to you when you have not asked for it, you can ask on that web site to be put on a do-not-mail list.

Companies waste money when sending stuff to people who definitely don't want it. They save money by having their mailing lists purged so they are only mailing to people who may want to buy. It is in the interests of the Direct Mail industry to know that you don't want the stuff sent to you.

Alice