[Exim] Changing incoming mail port

Hi

We are trying to set up trend interscan using exim3.22.
This software receives mail on port 25 then scans it then passes
out on a different port.

Once the mail has been scanned it needs to be picked up by exim
and delivered, but exim picks up mail on port 25. Is there any way
we can change that.

Any help would be greatly appreciated.

Thanks
Cheers
sherona