[dennisgorelik]

It is very expensive to work with out-of-date email list. If emails address bounced or, especially, if potential recipient is known for clicking "spam" button, then sending email to such recipient significantly lowers bulk email sender score.

I use a rule of thumb that every "spam" click costs me (as a bulk email sender) about $10. If somebody already unsubscribed -- it is quite likely that the next time they receive similar email -- they will click "Spam" button (which would cost me $10).

So I try to process "Unsubscribe" clicks quickly.