openICEM is a highly scalable server software that aims to provide a certified email service as specified by Italian law. It is based around the Postfix MTA, python-ldap, and python-clamd. It makes use of XML-RPC for communication among servers and does not require any shared service or shared filesystem.
Engroup is an enterprise groupware system promotes collaboration among members in a team or company. It also helps members manage their business better. It has the following modules: a dashboard that aggregates contents from the mail system and RSS from some known sources; private messages, an alternative method for fast communication among members to replace chatting or email; email, which supports the IMAP protocol with SSL enabled; a forum, implemented with JForum; a wiki, implemented with JSPWiki; HRM to manage employee information; CRM to manage customer information; a document management system; a project management system; a todo list to track private tasks of a user; and an RSS reader.
Mover is a system designed to move mail while eliminating as much metadata as possible. In fact, it eliminates virtually all metadata, except for the order and possibly the time that a message arrives at a given site. Addresses are encryption keys. The encrypted messages are sent to all mover locations. The intended recipient uses their key to decrypt the message.
smtp-cli is an SMTP command line client with support for advanced features such as STARTTLS, SMTP-AUTH, or IPv6. It also has scriptable message composition capabilities supporting anything from simple plain-text messages right up to building complex HTML emails with alternative plain-text part, attachments, and inline images. It's also a convenient tool for testing and debugging SMTP servers' setups. smtp-cli can be used to check a given server's capabilities, to test your server's setup, or to create and dispatch email messages. The command line interface is intuitive, and everything is scriptable and can run in a completely non-interactive mode from scripts or cron jobs. smtp-cli is ideal for shipping log files from remote machines, running periodic mail delivery test loops, etc.
exJello is a JavaMail provider that connects to a Microsoft Exchange server (actually, it uses the WebDAV interface exposed by Outlook Web Access). It is designed as a drop-in replacement for the standard POP3 and SMTP providers. This allows you to send and receive messages through your Exchange server in situations where a POP3/SMTP interface is not available (through a restrictive firewall, for example, or if your administrator simply does not provide a POP3 or SMTP gateway).
Scandalo is a very efficient and fast mail frontend for the clamdscan virus scanner. In other words, it is a simple mail filter that works as a wrapper for clamd, the famous Clamav antivirus daemon. Once integrated in maildrop or any MTA or MUA, it can quickly read messages and send them to the clamd process for virus scanning using the clamdscan utility. When a virus is found, the message is marked with a header, so you can easily set up your mail filter or MUA to drop, quarantine, or move the infected message to a mail folder.
Inbucket is an email testing service. It accepts messages for any email address and makes them available to view via a Web interface. It allows Web developers, software engineers, and system administrators to quickly see the emailed output of their applications. No per-account setup is required. Mailboxes are created on the fly as mail is received for them, and no password is required to browse the content of the mailboxes.