Addresses is a GNUstep address book that consists of a full-featured address book manager application, a source-code compatible replacement for Apple's AddressBook.framework (for accessing and manipulating address data programmatically), a framework of view/editor classes that make it easy to use Addresses from your own programs, and a number of tools. It is easy to use by both users and programmers and can store almost all imaginable data, including multiple phone numbers, emails, and addresses, photos, AIM/Jabber/ICQ/Yahoo IM details, and notes. It supports drag-and-drop and integrates well with GNUMail.
Bayesian Pattern Filtering Library is a general purpose library designed for building Bayesian Filters. Its primary purpose is to provide an easy-to-use interface to allow the building of Bayesian filters regardless of the data being analyzed. A user will only need to provide a tokenizer, hash function, and comparison function in order to build a Filter.
Buffy displays a window with a summary of your mailboxes and lets you open them in your mail program. It is written with the intent of being a handy everyday tool for people working with large volumes of mail. For mutt users, it can be a nice front-end to supplement the simple built-in folder browser when one has many folders to keep track of. It tries hard to work out of the box and looks for mail folders in sensible places and comes with reasonable defaults. It supports mail stored in maildir, mbox, and gzipped mbox format.
Buni Meldware Communication Suite is an enterprise groupware product providing an email server, calendar server, and a Web mail client. The Web mail portion is written using Adobe's Flash and provides a rich cross-browser experience. Protocol support includes IMAP, POP, SMTP, iCAL, WCAP, and more. It uniquely supports full database email storage as well as file system storage of emails on major database platforms, and is easily installed via a Web Start graphical installation process.
Claros Mini is a multi-protocol (POP3/IMAP) Web mail client with a user interface that is specially designed for devices with small screens. It can parse HTML and extract text to reduce the size of messages. The installation process takes less than two minutes, and no database setup is needed.
Quotient is multi-protocol (SMTP, POP, IMAP, SIP, HTTP, Q2Q) server that helps with all your online conversations, be they over email, IRC, IM, mailing lists, or voice over IP. It is written in Python on the Twisted framework, and uses Xapian for search and SpamBayes for spam classification.
Domain Technologie Control (DTC) is a Web-based control panel for hosting that can delegate the task of creating subdomains, email, and FTP accounts to users for the domain names they own. It has support for many programs, including bind 8 and 9, MySQL, Apache, PHP 4, qmail, Postfix, Courier, Dovecot, ProFTPD, Webalizer, and mod-log-sql. It can also generate backup scripts, calculation scripts, and config files using a single system UID/GID, and monitor all traffic accounting per user and per service. It is fully skinnable and translated into several languages.
Dovecot is an IMAP server whose major goals are security and extreme reliability. It uses index files to optimally store the mailbox state, which makes it very fast even with huge mailboxes. Indexes won't prevent external mailbox updates, so Dovecot is still fully compatible with standard Maildir and mbox formats. There's also a fully featured POP3 server included.