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.
GNU Mailman is software to help manage email discussion lists and e-newsletters. Its integrated Web interface provides easy-to-use access for list members and list administrators. Mailman supports built-in archiving, automatic bounce processing, content filtering, digest delivery, spam filters, topics, Usenet gateways, and more. It is fully internationalized, and supports digests and email commands. It runs on any Linux or Unix-like operating system and is compatible with most email and Web servers, mail readers, and Web browsers.
mailq_applet is a GNOME 1 panel applet that shows the status of your outgoing mail queue. It's intended for dialup users who may connect, wait for the queue to drain, then disconnect. Having this on your panel is much more convenient than running mailq over and over again from a terminal. It works with Exim and Sendmail. If you use a different MTA, you may need to make some changes, but the code is so trivial that that shouldn't be difficult. This code is no longer used or maintained by its author.
MailSpammer is a simple mailing list manager for smaller e-mail lists, using procmail and Perl. MailSpammer does not require administrator access, aside from initial setup (creating e-mail aliases), and features subscription, unsubscription, moderation, and archiving. The goal is not to be a majordomo-alike mailing list manager, but instead to provide a lightweight way to handle basic list management tasks.
MailWatch is a program for analyzing mail traffic. As each message is received, Mailwatch records summary information about it. Later, it can generate a textual report, showing the number of posts during a time period, who the most prolific posters were, and what the most popular topics were. It is targeted at the end user who wishes to generate statistics for personal email or mailing lists.
Majordomo is a program which automates the management of Internet mailing lists. Commands are sent to Majordomo via electronic mail to handle all aspects of list maintainance. Once a list is set up virtually all operations can be performed remotely, requiring no intervention by the postmaster of the list site.