NEVER hit the button to tell them to take you off.
It's there to confirm that somebody "lives" there, so they can put the address on their "address for sale" list. They don't care what you think of them, and in all probability the "button" is a dead link anyway. It's just to tempt you to actually keep the mail open long enough to confirm that it was opened.
And even if you "find" them, what they are doing is "perfectly legal," there being no law against being an asshole. (Part of a Congressional Retirement benefit, I understand.)