Joel Spolsky has a good solution for spam:
“If the European Union can change the money that 300 million people use all on one day, we can change our email protocol. Let’s find a protocol with decent authentication and with micropayments to make spam uneconomical, and let’s set a deadline, maybe two years in the future, when SMTP will simply be turned off. Everybody will know it’s coming, just like Y2K, and everybody will have to be ready.” — Joel Spolsky