[Exim] rejecting based on HELO

More and more of the spam I receive is sending the HELO line with *my*
IP address. In the Received headers this is easy enough to see and
auto-delete, but I want to be able to reject at recipt time - that is if
the actual IP address doesn't match the stated IP address, I want to
reject the mail.

Any guidance on this?

Please cc me on any responses.

Billy