GNU Anubis is an SMTP message submission daemon. It represents an intermediate layer between the mail user agent (MUA) and mail transport agent (MTA), receiving messages from the MUA, applying to them a set of predefined changes, and finally inserting modified messages into an MTA routing network. The set of changes applied to a message is configurable on a system-wide and per-user basis. The built-in configuration language used for defining sets of changes allows for considerable flexibility and is easily extensible.
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.
Mailfilter is a flexible utility to get rid of unwanted spam mails, before having to go through the trouble of downloading them into the local computer. It offers support for one or many POP accounts and is especially useful for dialup connections via modem. You can define your own filters (rules) to determine which e-mails should be delivered and which are considered waste.
Bogofilter is a Bayesian spam filter. In its normal mode of operation, it takes an email message or other text on standard input, does a statistical check against lists of "good" and "bad" words, and returns a status code indicating whether or not the message is spam. Bogofilter is designed with fast algorithms (including Berkeley DB system), coded directly in C, and tuned for speed, so it can be used for production by sites that process a lot of mail.
amavisd-new is a high-performance and reliable interface between MTAs and one or more content checkers, including virus scanners, and/or the Mail::SpamAssassin Perl module. It talks to an MTA via (E)SMTP or LMTP, or by using helper programs. No timing gaps exist in the design, which could cause a mail loss. It is normally positioned at or near a central mailer, not necessarily where the user's mailboxes and final delivery takes place.
Email Security through Procmail (the Procmail Sanitizer) provides methods to sanitize email, removing obvious exploit attempts and disabling the channels through which exploits are delivered. Facilities for detecting and blocking Trojan Horse exploits and worms are also provided.
Tiger Envelopes makes encryption automatic with almost any email program, allowing you to continue reading and writing mail the way you always have. It installs with one click on Windows, Mac, and Linux. It automatically configures Outlook, Outlook Express, Thunderbird, Mac Mail, and KMail. Tiger is a personal mail proxy server with automatic encryption. It uses POP3, IMAP, and SMTP to work with almost any mail client, crypto plugins to work with almost any type of cryptography, and Java to run on almost any operating system. Plugins for Bouncy Castle, GPG, and PGP are included.
The Heirloom Toolchest is a collection of standard Unix utilities. It was derived from original Unix material released as open source by Caldera and Sun, and contains multiple versions of each utility corresponding to SVID3/SVR4, SVID4/SVR4.2MP, POSIX.2-1992/SUSV2, POSIX.1-2001/SUSV3, and 4BSD (SVR4 /usr/ucb). It processes lines of arbitrary length and in many cases binary input data, supports characters in UTF-8 and many East Asian encodings, and contains more than 100 individual utilities including bc, cpio, diff, ed, file, find, grep, man, nawk, oawk, pax, ps, sed, sort, spell, and tar. Extensive documentation is included.