Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.
mailcow - An open source mailserver suite.
Alpine - Alpine is a fast, easy to use email client that is suitable for both the inexperienced email user...
Roundcube - Web-based IMAP email client
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.