I noticed a while ago that my spam filter was 100% accurate on all plain-text emails. Spammers are now forced to use obfuscation techniques like embedded images and HTML. It seems to me that this provides an easy way of totally eliminating spam:
- Bounce anything that is not from a whitelisted sender and contains an non-plain-text MIME section.
- Auto-whitelist anyone I send a mail to.
This means that anyone I email is free to send me whatever they want. Anyone can still contact me, but they are restricted to sending me plain text for the first email, until I reply to them.
Of course, spammers could start sending out messages saying 'I tried to send you some spam but your filter blocked it, please email me.' These will be caught in grey-traps for 8 hours, and by the end of the 8 hours there's a very good chance that the email will have been caught and the sender added to an RBL.
I'll probably try implementing this when I have time, but if anyone has time before me then please do and let me know how well it works.