Filters that fight back
Paul Graham with another brilliant idea:
If widely used, auto-retrieving spam filters would make the email system rebound. The huge volume of the spam, which has so far worked in the spammer’s favor, would now work against him, like a branch snapping back in his face. Auto-retrieving spam filters would drive the spammer’s costs up, and his sales down: his bandwidth usage would go through the roof, and his servers would grind to a halt under the load, which would make them unavailable to the people who would have responded to the spam.