I'd say Mail-in-a-Box, along with Modoboa and iRedMail, are perhaps the only serious open source email server setups right now, that are not based on Docker. Commercial ones do exist in the form of cPanel and Plesk (if you need some sort of support), although the underlying software is pretty much the same.
The only downside with MiaB is it is unnecessary complicated to update (both the software AND the server OS). This shouldn't be too hard to address in the future...
The only downside with MiaB is it is unnecessary complicated to update (both the software AND the server OS). This shouldn't be too hard to address in the future...
References:
https://modoboa.org/en/
https://www.iredmail.org/