This paper looks at the major spam filtering techniques in current use. In looking at methods both success rates and possible problems with each method are explored. Methods discussed include key word filtering, open relay filtering, open proxy filtering, dial-up filtering, non conforming mailing list filtering, cooperative sharing of spam samples, known spam origin filtering and Bayesian filtering.
I finished this paper in December of 2004 so the most recent techniques of both spammers and spam filters are not covered. Most crucial is the absence of coverage of image spam. Even with the slight age that this article has it will still be valuable to anyone trying to figure out how to minimize the amount of spam coming into their companies.