I’ve built my own mail servers before, though not from my residential ISP, so I have some idea what I’m getting into. I like that with MiaB, someone else is dealing with the config headaches. (o;
SSL certs won’t provision. See:
To get MiaB to generate a new DKIM key, I had to erase /home/user-data/mail/dkim/mail.private before running the setup.