Postfix, Dovecot, MySQL (MariaDB), postgrey, spamassasin.

Tips:

• once you get it running, keep close control and be prepared to shut down when the spam hounds find you.
• Do set up dmarc, dkim, and spf
• Put your server on spamhaus.org
• Don’t start if you’re feeling lazy, this will take a lot of mental attention.

I did mine before LLM’s, so I can’t comment how useful this will be, but I worry one might not understand the decisions made.