hMail Server - hMailServer is a free e-mail server for Microsoft Windows.
Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
mailcow - An open source mailserver suite.
PowerMTA - PowerMTA is an industrial-strength software for high-volume email delivery.
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.
Emails - Simple, easy and secure mail server with a convenient and simple interface.