protocol verified
How the proxy is reached
The protocol spoken to the proxy that owns the public address.
In detail
Seven characters of column, which fits the short names of the usual candidates. The combination that matters is this plus bind_ip and connect_ip: bind locally, connect to the proxy, and mail leaves from an address the node does not have. Worth comparing with our own proxy gateway before we build anything for MailerQ — the mechanism here is inside the engine, ours is outside it.