getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
Mahogany is a GUI email client for the X11/Unix, Windows, and Mac platforms. It supports a wide range of Internet protocols (IMAP4, POP3, ESMTP, NNTP) and encrypted communications using SSL, includes full MIME support, and aims to be fully standard-compliant. It allows the use of unlimited number of servers, supports filters and identities, and offers optional HTML viewing and much more.
The SeaMonkey project is a community effort to develop an all-in-one Internet application suite. It contains an Internet browser, email and newsgroup client with an included Web feed reader, HTML editor, IRC chat, and Web development tools, and is sure to appeal to advanced users, Web developers, and corporate users. It uses much of the Mozilla source code powering such successful siblings as Firefox, Thunderbird, Camino, Sunbird, and Miro.
tkbiff allows arbitrary commands to be executed upon mail reception. If you like programs such as xbiff and xbiff++ but wish they were more flexible, then you'll like tkbiff. Unlike other biffs, tkbiff is fully customizable. tkbiff also doesn't waste your valuable screen space with icons; instead, it shows you the mail itself. It supports UNIX, Mac, and Windows, IMAP, POP, and UNIX-style mail files, and SSL and APOP.
Distributed Checksum Clearinghouse (DCC) is a system of clients and servers that collect and count checksums related to mail messages. The counts can be used by SMTP servers and mail user agents to detect and reject bulk mail. DCC servers can exchange common checksums. The checksums include values that are "fuzzy", or constant across common variations in bulk messages.
Roundup is an issue-tracking system that is simple to use and simple to install. It has command-line, Web, and email interfaces. It manages a number of issues (with flexible properties such as "description", "priority", and so on) and provides the ability to submit new issues, find and edit existing issues, and discuss issues with other participants. The system facilitates communication among the participants by managing discussions and notifying interested parties when issues are edited.