[exim] RCPT acl tests

My exim server listens on localhost and the external interface, and on
ports 25 & 587.

There are therefore 4 combinations available for connections. It strikes
me that testing for these in an ACL would be useful; for example the
only time I want to accept email "From:" an external address is when it
arrives on the public IP, port 25.

In pseudo-code, I want to "ACCEPT if Src=remote, Dst=public:25, Auth=no,
From=non-local domain, To=local domain" (followed by "REJECT
From=non-local domain") in order to represent "normal incoming email"
and avoid relaying.

However, I can't see the ACL conditions that would allow me to test for
the destination IP/port ... how can I do this?

-jim