mail2news-easy is a utility that converts mail to news and news to mail. This program is unique in that it needs less configuration and modifying files than other products; it needs only one file, containing the signature of the mailing-list sender and the news name to which it relates. It installs easily, suppressing 100 of 100 modifications in the first install, and 75 of 100 when upgrading.
Maildrop is a powerful email filter/delivery agent. It supports mbox-style mailboxes and maildirs (a mail storage format used by Qmail). Its mail filtering language supports RFC822 parsing and GDBM/Berkeley DB database files. The maildrop package also includes a command-line tool to perform various operations on MIME messages.
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.
MIMEDefang is a flexible MIME email scanner designed to do all kinds of email processing, including anti-virus scanning, anti-spam scanning, replacing parts of messages with URLs, adding boilerplate disclaimers, and so on. It can alter or delete various parts of a MIME message according to a Perl-based policy filter. It can also bounce messages with unacceptable attachments and modify SMTP response codes on the fly. It works with the Sendmail 8.11 and newer "Milter" API, which makes it more flexible and efficient than procmail-based approaches.
mod_mocrify provides a handler to remove unnecessary whitespace from HTML pages before they are transmitted. It also is capable of making your HTML source virtually unreadable to human eyes by replacing all displayed characters with their ASCII code entity representation. All these modifications do not affect the layout in any way.
Heirloom mailx (formerly known as "nail") is derived from Berkeley Mail and provides the functionality of the System V and POSIX mailx commands. Additional features include support for MIME, IMAP (including caching and disconnected use), POP3, SMTP, S/MIME, international character sets, maildir folders, message threading, powerful search methods, scoring, and a Bayesian junk mail filter. Mailx can be used as a mail batch language in nearly the same way as it is used interactively. It can thus act as a mailbox filter, can fetch mail from remote accounts, and can send files as attachments.