ifile is a general mail filtering system that works with a mail client to
intelligently filter mail according to the way the user tends to organize
mail. ifile uses the machine learning algorithm Naive Bayes to classify
e-mail documents.

ifile is different from other mail filtering programs in three major ways: 

   1.ifile does not require you to generate a set of rules in order to 
     successfully filter mail 
   2.ifile uses the entire content of messages for filtering purposes 
   3.ifile learns as you move incorrectly filtered messages to new mailboxes 

ifile is not dependent upon any specific mail system and should be adaptable
to any mail system which allows an outside program to perform mail
filtering. The download package includes instructions for using ifile with
NMH, EXMH and slocal.  Grant Taylor describes the use of ifile with
procmail.

WWW: http://www.ai.mit.edu/~jrennie/ifile/