Simpler and cheaper

DENY from [IP range of China, Japan, Spain, Tiscali, Latin America, Quebec, Korea, Thailand, and if you don't expect traffic from the USA, them too]

The result is Balkanization of the Internet, from one point of view; from my point of view, it's quarantine of the major spam sources. I have cut my networks' spam uptake by over 95% this way, without losing any legitimate email.