Thirded, only with qmail. I know mine is a tiny private server, but scaling up would only require more hardware and minimal increase in hours working on it. OTO

Thirded, only with qmail. I know mine is a tiny private server, but scaling up would only require more hardware and minimal increase in hours working on it. OTOH, I manage hosted mail solutions for three other domains, and those all require more time, because I'm supporting other people.