Alternate meaning of opt-in

The stupidity of spammers never fails to amaze me. This is an excerpt from an actual e-mail I just saw:
This email is sent in compliance with strict anti-abuse and NO SPAM regulations. The message was sent to you as a response to your ad, an opt-in opportunity, your address was collected as a result of you posting to one of my links, reviewing your web site, you answering one of my classified ads, you have sent me an E-mail, or you unknowingly had your e-mail added to an opt-in mailing list.

(emphasis mine)

In other words, it’s spam. I wasn’t aware of this alternate meaning of the term “opt-in” until now. Brilliant.