SPAM isn't the problem. It's just the volume of legitimate email. David Gelernter in the Weekly Standard has a great write-up on my email overload problem (okay, yours too) and offers some possible solutions. (via Many2Many)
Sheer volume has turned email into an unreliable medium. Spam to the side, there is already too much (honest, legitimate) email for people to manage, and so they overlook messages or forget to answer them, in consequence of which conversations peter out into nothing--and no one is quite sure why, or what to do next. Excessive email volume is a fact of life and is never going away. The threat--which is guaranteed to force a massive retreat from this spiffy new medium within a few years unless we solve it--is the growing opacity of email, the Black Hole problem. If you haven't encountered it yet . . . just wait. Spam makes it worse, but it was a problem before spam and will remain long after spam is cured.
Here's how it works. You get an email (maybe longer or more complicated than average, or from someone you don't know); you have no time to respond right now, but you mean to answer--but other emails stack up, and you answer those first--but you still plan to reply--but more emails keep arriving. . . . Meanwhile the sender is wondering: Is he ignoring me on purpose? (I'll cross him off my list and forget about it.) Did he mean to reply, but has since forgotten? (Resend my message.) Or does he still mean to reply and just hasn't gotten around to it? (Don't get mad or resend.) All three possibilities are real, and happen all the time.
As volume rises, more email conversations trail off into nothing for unknown reasons, the medium is devalued further, and the problem gets worse--people set even less store by a mail message, send one out on even less provocation, volume rises, more email conversations trail off into nothing for unknown reasons, the medium is devalued even further.