Anti-Spam provisions in sendmail 8.8.Howto guide to configure an anti-spam filter.

MasqMail is a mail server designed for hosts that do not have a permanent internet connection eg. a home network or a single host at home.

Mutt is a text-based e-mail client, similar to Elm and Pine.

Business-class messaging and collaboration for Linux and UNIX. Supports scheduling and other rich Microsoft Outlook functionality via MAPI, as well as internet e-mail standards like IMAP4rev1 and LDAPv3.

Samsung SDS's business messaging and collaboration / unified communication product, based on HP OpenMail.

Sandmail, an email client for linux using GTK.

Free, open-source producer of dynamic signatures for e-mail and news postings. Allow signing messages with a different .signature every time.

The GTK+ Email Client