Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
mailcow - An open source mailserver suite.
WildDuck - Self hosted modern mail server
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.
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.
Emails - Simple, easy and secure mail server with a convenient and simple interface.