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.

Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.

Microsoft 365 - Boost your productivity with reliable access anywhere with services like email, calendar, file sharing, meetings, instant messaging, and Office Online

mailcow - An open source mailserver suite.

Envigeek Digital Workspace - Business email can be more than just a mailbox. It can be a virtual office where all the team work and online meetings happen. You can create and edit documents there – alone, or in collaboration with your team.

Mail-in-a-box - Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software and also includes contacts and calendar synchronization.