Yahoo and their mail filters..

[johnl at iecc.com (John Levine)]

>Nor should they.  Anyone who actually researches this stuff knows that  
>the vast majority of "unsub" links simply confirm you as a live target  
>who will click on random links sent to them through e-mail.   

That's the conventional wisdom, not confirmed by research.  The FTC
tried it in 2002 and found that opt-out made the spam load drop
slightly, and I don't see any reason to think it would be different
today.

http://www.wired.com/techbiz/media/news/2002/04/51517

R's,
John