[Exim] SMTP to a dynamically allocated IP?

Hi all.

Thanks to Tabor for your help with M$Exchange. All sorted now.

Problem is, my 2nd tier provider has moved to a
completely dynamic network now ie. no more static ip addresses.

My other M$Echange client is running his server on a machine with
a sub-domain, and dialing up to retrieve mail - so obviously he
gets a dynamic IP. I tried (hahahahahaha) to capture his IP as
he came in to deliver mail to that IP but as you can imagine it
failed big time!

Don't suppose anyone knows of any way to make Exim capture a
dynamic IP and "magically" map that against a clients sub-domain
and then deliver mail to it do you?????

Ken.