[Exim] Passwd file authenticator

All,

I'm trying to configure exim 4.24 to force authentication from clients such as Outlook using the passwd file on my server.
Unfortunately, the documentation is very detailed about everything except how to get it working!

I basically want it to fail to relay mail from that IP if the user isn't authenticated correctly.

Can someone provide me with an example for the exim.conf file

Thanks

James