I haven't tried it, so it might be more complicated than the documentation leads me to believe, but Mox looks promising: https://www.xmox.nl/

I've been using it for a year now. Can vouch for the quality and reliability

I use Postfix and Dovecot. Configuration was annoying, but doable. If you read mail on the server itself then you don't need Dovecot.

Proxmox has a mail appliance.