Peter - welcome to the wonderful world of Spamvertising (advertising using barely legal or possibly illegal e-mail strategies). Never unsubscribe from an unknown source - it simply indicates to the spammer that you are watching your inbasket. They may unsubscribe you but they will add/sell your e-mail address to dozens of other 'helpful' marketing entities and the cycle starts again.
You have 2 choices...
1. Change your e-mail address to something new and tell your legit contacts, or
2. Enable spamvertising blocks or switch to a spam filter that is effective against spamvertising
FYI, spamvertising is mostly image based marketing. Often the message is made up of many images (even the text) to defeat antispam content scanners. Spamvertisers buy, use and discard e-mail domains (once they are black listed) in their campaigns. They run professional marketing campaigns that track deliveries rates, open rates, click through rates, etc. - they are paid to pollute your in-basket. The good news is that their messages are detectable and blockable.
Disclosure - I work for perfectmail.com and we stop spamvertising. If you run your own mail server, try our free edition (www.perfectmail.com). Otherwise, turn up the spam filters and never unsubscribe to an unfamiliar list.
Now, for junk snail mail... look for junk advertising material that has a return envelope with pre-paid postage. If you get one, tape a brick to it and mail it back to the advertiser.
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