On the other hand, I've been hosting my own E-mail (exim and dovecot) on a $5 VPS for the past 15 or so years, and it's pretty much set and forget. The most maintenance I have to do is when certbot fails to renew my ssl certificates and I have to manually go in and babysit it, but that's certbot/LetsEncrypt's fault, not the E-mail software. I have maybe had deliverability problems twice in those many years.