I have been using modoboa, my installation is fine as far as it goes, but coming up a little short technologically these days, and the upgrade path is total replace. If you have or install Docker on your server, there are poste.io and docker-mailsever,which both look good. Running your mailserver in a container or VM is almost essential, for security, and so you can blow it away and start over if you make a mistake.
Running an email server is not necessarily hard, but it is stressful: if you have other users, even family, they will take it for granted when it works, and complain loudly when it does not. Like any server that others use. But, beyond security, I have a certain stubborn geek machismo about it, it’s a level of sysadmin above basic.
Has anyone here used Mox? It looks interesting, but maybe a little immature.