[Exim] Relaying and POP server ...

Here is my question again :-))

I'd like to allow my POP clients to send mails through exim.

Is there a way to do it ?

I suppose the way to do it is to log the user login (and IP adress) in a log
file, and then ask exim to check this IP before allowing or denying the
relay (with a timeout) ...

Any way to do it ? Any existing tools ?

Georges