SpamOracle 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.
SpamProbe is a fast, intelligent, automatic spam detector using Bayesian analysis of word counts in spam and non-spam email. Intended for use with procmail to filter inbound email. No manual rule creation required.
spamresponder is a very simple and radical spam filter, combining dns-validation with the challenge/response approach.
SpamTestBuddy is a simple, light-weight, multiple-input spam scoring tool. It is standalone and can be used with simple procmail rules without root access or daemons. Features built-in support for simple DNS checks including DNSBL (DNS-based blocklist) queries, and can scan headers from filters such as SpamProbe, QSF, DSPAM that you already use.
Simple Procmail Anti-Spam Templates: an easy to use, but powerful, set of e-mail filters to deal with Unsolicited Commercial E-mail (UCE), aka spam, using the most excellent procmail program
SPF Sendmail milter
SPF Sendmail milter is a simple Sendmail filter that implements the Sender Policy Framework with the help of the libSPF2 library. It checks SPF records to make sure that the email is authorized by the domain name from which it originates. This prevents email forgery, commonly used by spammers, scammers, and email viruses/worms. It can reject messages on SPF hardfail result. Also, it adds the standard Received-SPF header with SPF results to the scanned messages.
spmfilter is a mail filtering framework. It attempts to be a general filtering framework for any purpose.
Sporkie is a challenge/response spam email filter. It uses CAPTCHAs (randomly generated, distorted images of numbers) in order to verify that a person sending email is human. It works in the same manner as the ASK project, except that Sporkie uses CAPTCHAs. The main advantage to using CAPTCHAs is that it catches automated spam bots that don't spoof their email address. With ASK, such bots would get through the system. Sporkie is provided under the OSCL Type-C license.
a Python based spam filter for Sendmail that utilizes spambayes heurestic spam filtering and virus scanner (BitDefender, not included). You also need Python Milter and Spambayes
The SpamBouncer is a spam filter that runs under Procmail, a Unix-based email processing program. It filters and classifies your incoming email, moving spam to a separate folder or deleting it entirely. This allows you to find your real email without having to read through a flood of spam first.
wl is an email "filtering" program: it reads an email on standard input and writes it back out on standard output. If certain criteria are met based upon the headers of the email, an X-Whitelist or X-Blacklist header will be added to the email.
Zabit is a content/attachment filter for qmail. It's been coded in C language for performance reasons.
Zmscanner is an extensible modular contentfilter for Zmailer and Sendmail MTAs (sendmail code is still experimental). It is designed to be fast and efficient and thus suitable for high traffic mail systems.