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.
Elm Millennium Edition is a text-based mail client. There are two branches: Elm 2.4ME+, which is based on Elm 2.4, and Elm ME+ 2.5, which also incorporates some code from Elm 2.5. Elm Millennium Edition contains enhanced MIME and character set support. A subset of UTF-8 (Unicode) is handled. It can read mail from a local mbox and POP and IMAP folders and can pass mail to the PGP or GPG programs. It can also view digests as a mailbox and reassemble fragmented (message/partial) messages. It includes modules for TLS/SSL, iconv, and SMTP.
The PortalSys Addressbook is designed for clients who use Outlook on the desktop but use Linux as the mail system. It allows you to easily integrate Outlook with your Linux system's addresses. The system is made up of two parts: an Outlook service for your Win32 clients and a server-side application to generate and update your addressbook as often as you like.
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.
RFC 2015 defines a proposed Internet standard for sending PGP-encrypted email. This PGP/MIME has been incorporated into several MUAs such as Mutt and (with the AEGYPTEN project) KMail. However, a lot of email clients still don't support it. pgp-mime-handler can decrypt/verify such messages via a pipe, so it can be used as an email filter in many programs or scripts.