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.
hMail Server - hMailServer is a free e-mail server for Microsoft Windows.
Microsoft 365 - Boost your productivity with reliable access anywhere with services like email, calendar, file sharing, meetings, instant messaging, and Office Online
Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
YouTeam - YouTeam is a new, smarter way to outsource.
PowerMTA - PowerMTA is an industrial-strength software for high-volume email delivery.