Nice bit of anti-anti-spam - check this url out:
URL "spoof" a go-go.
The problem is that everyone wants a fool-proof way of defeating spam, while keeping e-mail open to all. Is that mathematically possible? For me, the problem isn't choosing which mail to block, but how to inform non-spammers that you've blocked their mail. I currently don't send a response as it increases mail quantity, which I'm not keen on.
Technically, is there any difference between an unknown person sending an e-mail to a public e-mail they received (effectively) randomly, and a spammer?
I might just bounce any non-white-listed mail to me, with a "failed" error (I consider that ok...), and rely on Google for people to get in touch with me.