[Exim] Rejecting all mail apparently from a particular domai…

Is it possible to set exim to reject all that apparently comes from
@domain.com unless its from a specific IP address ?
I have a client who fears that other people can forge the from: address.
So, he wants me to reject any mail coming to my server with a from address
of his domain unless the previous hop
is his mail server.


Rgds
TDN