SpamOracle, a.k.a. "Saint Peter",
is a tool to help detect and filter away "spam"
(unsolicited commercial e-mail). It proceeds by statistical analysis
of the words that appear in the e-mail, comparing the frequencies of
words with those found in a user-provided corpus of known spam and
known legitimate e-mail. The classification algorithm is based on
Bayes' formula, and is described in Paul Graham's paper,
A plan for
spam.

This program is designed to work in conjunction with
procmail.
The result of the analysis is output as an additional message header
X-Spam:, followed by
yes, no or unknown, plus additional
details. A procmail rule can then test this X-Spam: header and
deliver the e-mail to the appropriate mailbox.