[Exim] How to get Exim 4.04 to verify that a sender comes fr…

    I would like to set up Exim to verify that all senders come from our
domain, and refuse the relay if they don't.  Is there a way to make it
verify the that the sender's address is *younglife.org?  I have read the
docs, but still can't figure out how to make it reject a relay based on
a sender address not meeting a spec.
Thanks for you help,
Tim Sexton