Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
mailcow - An open source mailserver suite.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Eudora Internet Mail Server - Eudora Internet Mail Server is a highly advanced internet mail system that supports the all kind of email systems and clients either it is IMAP, POP3, SMTP and much more.
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.
WildDuck - Self hosted modern mail server