Analysis of Spam, and a Proposed Solution
It always seemed to me the easiest solution to spam would be to make it illegal to forge the return address with big civil/punative damages otherwise. If the return address has to be either from the sender or the company they represent then it's easy to harass them to stop sending you messages. If it the return address is forged, you can bet there's lots of people that want to make money by finding out where who it's from and suing the crap out of them. Kinda like bounty hunters. There's no free speech issues since you can still technically email out any content you want. Obviously IANAL and also easily amused by shiney objects but it seems a simpler and cheaper solution than redesigning SMTP/throwing technology at the problem. If there's no money in spamming, it would stop.