Email spam is a huge problem. I have found for myself quite a simple solution, however it'll take some time to "migrate" completely over to it. The solution is to create a unique email address everytime I have to give an email address to someone else or to some website to sign up. If I want an account at twitter, I'd use "www.twitter.com@MYDOMAIN.COM". For webbased services, I use the full domain name incl. subdomain (www) on the left of the @ (some poorly designed websites do not recognizes the www. as valid email address, for those I just leave it away).