Do not be taken in by this. Talk is cheap, especially when someone else pays. The advertiser does not have the right to put you on their mailing list in the first place, and if you quietly remove yourself by mailing this address, you are helping to legitimise this mode of operation. If nobody complains, it will become accepted practice. If you find any companies which advertise such data or programs for sending unsolicited advertisements, it may be a good idea to let them know that they are providing a service which is not appreciated and to politely ask them to desist.
Spammers buy e-mail lists, and the addresses can be very old.
When this happens, repeat the spam-hunting procedure, only with an even greater degree of righteous anger. Some spammers provide 800 numbers. It can be quite effective, and is almost always quite satisfying, to call and give them a piece of your mind. Some spammers become abusive when you complain. Cc'ing their abuse to their post-master can work wonders.