[Exim] Using exim.conf to whitelist

I have been trying to find a way to use the exim.conf file to deny
everything except emails in a file (or listed in exim.conf if need be).
I've only half figured it out and I can't really get it to work the way
I'd like. The biggest issue I'm having is that I only want the whitelist
to apply to one user. Has anyone done this before, or have some pointers
they could give me? It would be much appreciated. Thanks

-dema
www.haxors.com