[exim] authentication

Hi,
i have running an exim4 on a debian 3.1 system. I sends, receives and
relays everything, i want. Just the relaying is known as a big problem.
To prevent unwanted spam over the machine, i would like to use
authentication at smtp connections through the clients. Well, how can i
prevent exim4 to accept mail from unauthenticated clients?

greatings,

--
Michael Rouba

CSP-Berlin
Consulting - Systembetreuung - Printmedien

#!/bin/bash
#
# Diese Mail wurde Ihnen präsentiert
# mit freundlicher Unterstützung von
# Debian GNU/Linux
#