The software side looks like someone just executed an ancient Postfix + Squirrelmail + Dovecot tutorial[0] and cobbled together a horrible UI for it.
[0]: https://www.exratione.com/2012/05/a-mailserver-on-ubuntu-120...
[0]: https://www.exratione.com/2012/05/a-mailserver-on-ubuntu-120...
I guess, at least it isn't running it in conjunction with sendmail https://threatpost.com/no-fix-for-squirrelmail-remote-code-e...