[Exim] How to allow only outbound relaying with exim 4.0?

Greetings. I have a server running Exim 4.05 which is supposed
to server as an outbound relay for one specific network. There
should never be incoming mail, outbound mail to anywhere from the
specific network should always pass through. The config I'm using
is clearly not working, it's acting as an open relay. Can someone
explain to me how to use acl_check_rcpt: to allow relaying only
from my one specific net, to anywhere?

TIA!!!

Judith Reed
jreed@???