Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
mailcow - An open source mailserver suite.
MailEnable - MailEnable is a Windows based mail server and email server program that is packed with the state of the features and functions like antivirus and spam filtering system, webmail management system, cardDAV, CalDAV and much more.
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.