Scientific American (April 2005) has a very good overview of techniques that are used to stop Spam: Stopping Spam [Information Technology] What can be done to stanch the flood of junk e-mail messages? (Vol. 292, No. 4, P. 42; Goodman, Joshua; Heckerman, David; Rounthwaite, Robert)

[Via ACM News Service: April 22, 2005]