Amavis

Amavis Mailfilter

SOGo

SOGo is a Open Source Webmail client

Modoboa

Modoboa is a Open Source email server using Amavis, Radicale and postfix

mailcow

mailcow is a mailserver running inside a docker, mailcow uses SOGo, ClamAV and more

PostfixAdmin

PostfixAdmin Is a gui for postfix, i never used it myself before, but maybe in the future it might be handy to have a look at it.