Some while ago I posted something about a new lookup...
It's called the ipdir (former dirlist) lookup.
It can be used to make exim check himself for the
spool files created by your popper.
Check it out. It works fine for me with exim 3.04.
I made the patch (and some readme stuff) available
under...
http://www.gwdg.de/~tcurdt/exim/exim-pop-before-relay.tgz
--
Torsten