[exim] External hosts relaying with my local user RHE3 box

Hi All,

My knowledge of exim is pretty basic, I have however got my head around rbl
lists and it seems to be working fine, however I can't seem to stop external
users from other hosts connecting to my box and sending / relaying mail from
its local users.

I am sure that there is a setting that can be changed to stop this and to
allow my apps on the box to send and relay, the external relaying is killing
my box performance at times and would appreciate any help or pointers to
securing my exim setup so that external users cannot abuse my system, I have
checked and it would appear that my box is not an open relay so I think it
is an authentication issue ....


I am not sure what to send in order to expand but if I can connect with
someone here that knows about exim then maybe I can supply what is required
to resolve the problem

Thanks in advance for any help offered.