[exim] Limit Inbound by Domain

In a hosting environment, Exim serves as the receiving MX host for multiple
domains. However, one of the domains (for which the Exim host is not a
registered MX) should only receive mail arriving via connections from
specific IP addresses/networks, in order to only accept mail relayed from a
spam-filtering service.

I've searched the docs and FAQ's and cannot figure out if some form of
sender_net_ statement or an ACL should be utilized -- or something else. How
can that be accomplished for one of the domains? Thanks.

Ron