Exim mail Gateway with recipients check for incoming mails

[Matthias Sutter]

Hello,

i have to setup a exim that should check for existing recipients. The 
recipients users data are stored in a flat text mail so i know witch 
users are homed on the local side.
Do somebody know how I to configure the exim, that he check for the 
incoming recipients and let all mails from the relay_from_hosts 
untouched/unchecked?

Sorry for the short problem description, but I don't know how to decribe.
Do somebody need more informations for help. Please conatact me.

Matthias