clapf is a high performance email content filter application. It includes a statistical (inverse chi-square) antispam module, an interface to several anti-virus products, and a Web UI (including a spam quarantine) written in PHP. It supports virtual users, URL- and IP-address blacklists, whitelists, LDAP directories, policy groups, minefield, and many more features. clapf can be used as an after queue content filter with Postfix (including as an appliance) and Exim or via the maildrop local delivery agent (LDA). It's also ideal to act as a spamfilter appliance in front of an Exchange server.
The milter module for Python provides a python interface to Sendmail's libmilter that exploits all its features. Milters can run on the same machine as sendmail, or another machine. The milter can even run with a different operating system or processor than sendmail. Sendmail talks to the milter via a local or internet socket, and keeps the milter informed of events as it processes a mail connection. At any point, the milter can cut the conversation short by telling sendmail to ACCEPT, REJECT, or DISCARD the message. After receiving a complete message from sendmail, the milter can again REJECT or DISCARD it, but it can also ACCEPT it with changes to the headers or body.
DSPAM is a server-side statistical anti-spam agent for Unix email servers. It masquerades as the email server's local delivery agent and effectively filters spam using a combination of de-obfuscation techniques, specialized algorithms, and statistical analysis. The result is an administratively maintenance-free, self-learning anti-spam tool. DSPAM has yielded real-world success rates beyond 99.9% accuracy with less than a 0.01% chance of false positives.
testmail is a Perl script that checks email availability at the POP3 server (including SSL), filters it according to the defined rules, and (depending on the selected method) gets the messages to the local mailbox and/or removes them from the server. It uses Perl Mail-POP3Client to establish POP3 connections, IO-Socket-SSL and Net-SSLeay modules for SSL connections, as well as MIME-tools module for decoding MIME encoded email fields.
SAGATOR is an email antivirus/antispam gateway. It is an interface to any smtpd that runs an antivirus and/or spam checker. Its modular architecture can use any combination of antivirus/spam checkers according to configuration. It currently supports ClamAV, nod32d, AVG, Sophos, TrendMicro AV, Symantec AV, Spamassassin, bogofilter, and quickspamfilter. It has some internal checkers (string_scanner and regexp_scanner). It can parse MIME mail and decompress archives.
LEPL is a recursive descent parser library written in Python. It is based on parser combinator libraries popular in functional programming, but also exploits Python language features. Operators provide a friendly syntax, and the consistent use of generators supports full backtracking and resource management. Backtracking implies that a wide variety of grammars are supported; appropriate memoisation ensures that even left-recursive grammars terminate.
GNU m4 is an implementation of the traditional Unix macro processor. It is mostly SVR4 compatible, although it has some extensions (for example, handling more than 9 positional parameters to macros). GNU m4 also has built-in functions for including files, running shell commands, doing arithmetic, etc. Autoconf needs GNU m4 for generating `configure' scripts, but not for running them.