Campaign Monitor - Email marketing software built for designers and their clients to run successful email campaigns.
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.
Yesmail - Yesmail provides email marketing solutions that integrate mobile, web, and social channels for marketers.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
MailPlus - MailPlus is a Dutch-based email marketing solution provider.
mailcow - An open source mailserver suite.