[Exim] questions

I installed Exim, and administrating a machine. The domain is,
moonshyne.net, I want remote users to be able to use the server as an SMTP
server in their mail client(s). Incoming mail works fine to moonshyne.net. I
want it so that when a user remotally sends MAIL FROM: user@???,
that it'll relay, but won't relay other non-local domains.