I've ran MTAs and MDAs both personally and professionally at scale. I've hosted my own postfix and dovecot instances for about 13 years now for one reason, sie

I've ran MTAs and MDAs both personally and professionally at scale. I've hosted my own postfix and dovecot instances for about 13 years now for one reason, sieve. I cannot live without it. Honestly, the original setup of everything is a big lift if you've never done it but once you have ldap+krb5/PKI for auth{n,z}, DNS working properly, and a working POSIX setup (what used to be sysadmin 101) it basically runs itself in perpetuity. The underlying tech is old, feature-complete, and rock solid. Not to mention you're in full control of the entire stack. I honestly haven't had an issue after the first year and I use email HEAVILY. Though to be fair, I do have a bunch of ldap entries and routing rules in place so the power users can choose sieve+dovecot and all the plebs can use the Gmail webui.