mailcow - An open source mailserver suite.
Jam.py Postfix Aliases - Web App to manage only Postfix Aliases with a LARGE number of managed Domains (>hundreds).
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.
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.
ViMbAdmin - ViMbAdmin (pronounced vim-be-admin and meaning Virtual Mailbox Administration) is intended as an...
NeutronMail - Self-hosted server for the ProtonMail client.