Spam filters have been successful only because enormous amounts of resources are continuously being spent on them. That's a constant drag on the IT infrastructure and online commerce in general. Spam filters are just a gigantic band-aid for an email system that is fundamentally flawed. If we weren't already so dependent on SMTP I don't think it would be considered a safe medium for conducting business, with its vulnerability to Spam, phishing attacks, and lack of authentication. The internet will never achieve its potential if you can't put your contact details on a web page without being bombarded with garbage. If the average person can't trust everything in their inbox then everything must be viewed with suspicion. Any message in your inbox could be faked. Markets are based on trust. Suspicion weakens the market.
We have the technology to make a better system. We just have to demand it. If a new system was created, that was free of Spam and phishing, how fast would people migrate to it? There's room for multiple instant messaging systems. There must be room for multiple email systems.