msmtp is an SMTP client with a sendmail compatible interface. It can be used with Mutt and other MUAs. It forwards messages to an SMTP server which does the delivery. Features include various SMTP AUTH methods, TLS/SSL-encrypted connections (including support for client certificates), support for multiple accounts, DSN, and IPv6 support.
GroupOffice is a groupware suite that takes your office online, implementing online collaboration and CRM. It allows you to share projects, calendars, files and email online with co-workers and clients. It is easy to use and fully customizable. It also features synchronization with PDAs and Outlook.
mpop is a small, fast, and portable POP3 client. Its features include header-based email filtering (filter junk mail before downloading it), delivery to mbox files, maildir folders, or a mail delivery agent, a very fast POP3 implementation, many authentication methods, and good support for TLS/SSL.
Cerb is a fast and flexible Web-based platform for business collaboration and automation. It helps you remember anything about anyone, collaborate from anywhere, deftly reply to a flood of email, automate, stay informed, capture feedback, track time, flag opportunities, manage tasks, share expert knowledge, and otherwise execute efficiently.
Dada Mail can help you manage a mailing list, offers complete support for safe, closed-loop opt-in subscriptions, sends out mass mailings, keeps an archive of your messages, and allows you to share your messages in many ways. It runs on your Web hosting account and you interact with it through your Web browser, making it available anywhere you have a connection to the Internet. You do not have to rely on a third-party list management system with costly monthly fees. It is rich with features, but tries to keep it simple. It is designed to favor flexibility, extensibility, and ease-of-use over core speed or extremely flashy but hard-to-use features. It is designed to be installed, set up, and understood by regular people who have Web sites, but has enough advanced features to entice more proficient users. If you've ever installed a bulletin board or blog software, you should be able to install Dada Mail without too many problems. Dada Mail can scale. You can install Dada Mail on most any basic hosting account and start sending out messages. If your mailing list grows large, you can switch to sending with a more powerful third-party system, like Amazon SES, where there's potentially no limit on the number of emails you may send, all without having to change mailing list management systems or your hosting.
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.
Bugzero is a Web-based change management and issue tracking system used in a distributed team environment to track software bugs, hardware defects, test cases, or any other issues. It can also be used equally well as a helpdesk customer support, trouble ticketing, or email management system to collect and manage customer feedbacks, incidents, requests, and issues. It is easy to use, but still flexible and adaptive, and can be configured to fit to your organization's unique business process and workflow.
Sympa is a scalable and highly customizable mailing list software. It can cope with big lists (780,000 subscribers), and it comes with a complete Web interface for both the user and the administrator. It is internationalized. Sites can customize Web and mail templates, authentication backends, and authorization scenarios. Dynamic mailing lists can use multiple backends (LDAP, SQL, files, lists, or others). Sympa is the only S/MIME and DKIM enabled mailing list software, and it provides both authentication and encryption.
Clam AntiVirus is an anti-virus toolkit designed especially for email scanning on mail gateways. It provides a number of utilities, including a flexible and scalable multi-threaded daemon, a commandline scanner, and a tool for automatic database updates. The core of the package is an anti-virus engine available as a shared library.