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.
mailcow - An open source mailserver suite.
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.
Roundcube - Web-based IMAP email client
Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.