You should not run your mail server because mail is hard.
https://poolp.org/posts/2019-08-30/you-should-not-run-your-mail-server-because-mail-is-hard/ [poolp.org]
2019-09-01 00:29
It is therefore very important that we don’t let the myth propagate further. Our best interest is to have a WIDE variety of mail hosts and providers, small and big, commercial and not. We must not allow the number of mail hosts to shrink, they must increase so the e-mail address space out of the control of Big Mailer Corps remains significant.
source: L