Huh, a great idea and it's demise...
It seems really exciting to me at first....
But I don't think, that trying to unsubscibe is such a good idea, it is a difference, if an email adress is actively used, or not, even if the amils don't bounce back.
If someone answers a email, that it has a higher value, because it shows, that the owner is concerned about it. He wouldn't be concerned about it, if the adress wouldn't be important to him.
So email traders can sell such "answering" adresses at a higher price...and so you would get even more spam, no?