Detecting spam just from HTTP headers(glinden.blogspot.com)
glinden.blogspot.com
Detecting spam just from HTTP headers
http://glinden.blogspot.com/2008/11/detecting-spam-just-from-http-headers.html
http://glinden.blogspot.com/2008/11/detecting-spam-just-from-http-headers.html
PG mentions this in his articles about Bayesian Spam filtering. Seems pretty compelling.