I'm trying to get Exim to work in a way that it rewrites messages that stay in the LAN differently than the ones that go out to external servers.
Just rewriting every message is possible, but that would clutter messages for local use.
Internal rewrite would be
*@*.localnet firstname.lastname@example.org T
And outgoing would be
Which would result in email@example.com becoming firstname.lastname@example.org?