Oh that does look interesting.
check out mailcow sounds like everything you need.
I am looking at setting up main-in-a-box for some time now. But currently I pay $2/mo for mailcheap shared plan. I used to use mxroute but didn’t like cpanel email.
https://poste.io/ is a great docker for setting up a mail server. I started using it to self-host my personal email accounts to Degoogle myself.