Be careful with that. People who sign up for mailings sometimes report them as spam once they get tired of receiving them, rather than politely unsubscribing. That can wind up getting you on any of the zillion spam blacklists out there.
It's actually a pet peeve of mine. If you no longer want to receive a mailing, then politely unsubscribe. It's simple. But some users are so ignorant, self-centered, or both that they have a really hard time with the concept that a piece of mail that they subscribed to doesn't magically become spam once they no longer want to receive it.