Nginx can be used to proxy several mail protocols. This can be useful in a variety of scenarios: load balancing, providing up-to-date TLS for servers that don’t support it, graceful server migration, or enabling user-specific storage policies.
Unfortunately, what’s not clear from the documentation is that nginx (at least at 1.18
) can’t proxy over encrypted connections - which makes this unworkable except in the case of servers on the local network.