[exim] Accept local mail only from certain IP or auth

Hello all,

I need an exim server to only accept local mail from a content filter (two
IPs) and not the entire internet. Right now, a spammer can figure out the
exim server's IP and bypass the content filter.

Using IPtables won't work because I still need exim port 25 open to the world
for relaying SMTP authenticated mail. It is part of a web hosting server.

Is there a way to force exim to accept local mail only from the content filter
if it is not authenticated?

Thank you.

--
Randy