The classic email sending library for PHP
mailcow: dockerized
Fast and easy-to-use webmail front-end for your existing mail server.
Zentyal is a Linux Small Business Server
Simple, modern & fast web-based email client
an 'auto-reply' bot for your mail server
An unofficial web console to administer Apache James 3 server
To synch and encrypt all sorts of data across different sources
Linux Mail Server with Calendaring and IM