I guess the real load with spam is on the infrastructure, not the end user; so any solution should target the infrastructure, not the receiver’s inbox. Venema is even harsher:

“In my personal opinion, the reliability of email reached its maximum near 1998; it has gone down ever since as the result of increasingly aggressive anti-spam/virus measures. This observation has led me to conclude that the spammers aren’t destroying the email infrastructure, it’s the well-meaning people with their countermeasures.”