django-cyradm

django-cyradm is a web interface to manage postfix controlling accounts, aliases and virtual…

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.

Mailpile

Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.

NeutronMail

Self-hosted server for the ProtonMail client.

Roundcube

Web-based IMAP email client

Virtualmin

It includes numerous features not in the GPL version (like script installers, resellers, HTML editor, an improved UI, mobile access, spam and virus filtering).

iRedMail

A fully fledged, free email server solution, an open source project (GPL v2).