I'm still running Sendmail on NetBSD, the way I've been running it since the '90s.

You'll find plenty of people telling you to not do it, but they mostly seem to think that others shouldn't do things because they can't.

The biggest problem with self-hosting email is deliverability, and it's easily handled by smarthosting through a reputable service, so anyone who says it can't be done hasn't really thought things through very much.