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.
Sendooway is a multi-user and multi-target ESMTP proxy that acts as mail transfer agent. Instead of configuring SMTP servers and authentication data for every mail identity on every device, it allows you to configure them centrally. Sendooway automatically uses the correct smarthost, logs on with the user's account data, and sends their mail.
pop3ml is a program to manage mailing lists and newsletters without a local SMTP server. It requires only a simple POP3 email account. It's highly configurable by users. You can subscribe or unsubscribe simply with email messages. There is optional subscription and unsubscription confirmation, subscription moderation, message moderation, digest message mode, parent/children list management, mail scheduling to postpone or repeat a message, a mail filter (with a procmail-like syntax), a message queue for unsent messages, message size check, a command to retrieve messages, bounce detection, message header management, black/white/allow/deny lists, and other functions. There is also a program to test list settings without sending any messages and another program to view and search through stored messages. You can configure it with programs like phpMyAdmin.
Mailpictures is a Nautilus extension in GTK/Perl, designed to be a more featured nautilus-sendto replacement. It allows direct access via Nautilus context menus, automatic resizing of pictures, setting for JPEG compression, ZIP archiving of the selection, support for Evolution, Thunderbird, Icedove, and Kmail, and the ability to save results in a folder.
Trojita is a Qt IMAP email client. It is a pure Qt4 application with no additional dependencies. It has a robust IMAP core implemented using Qt's Model-View framework. Standards compliance is a design goal. It has support for bandwidth-saving mode aimed at mobile users with expensive connections. In addition to the usual SSL/TLS connections, the server can be accessed via SSH. It has on-demand body part loading, offline IMAP support, and safe dealing with HTML mail (actually more robust than Thunderbird's).
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.
Yasma (Yet Another Sendmail Logfile Analyzer) is a reporting tool for sendmail log files. It provides a nice overview of your mail traffic like: messages transferred, some average values, top lists of messages sent, received, rejected, etc., and top lists of supposed spammers, status messages, relay hosts, and mailers. It analyzes one or more log files from the command line and writes an HTML report. For security, it can hide the user part of mail addresses listed in the report. A GeoIP database can be used to show country information.