[Exim] filtering based on to address

Hello,

Thank you for your previous help with Exim and auto-repsonders. My next
task is setting up filtering on certain email addresses.

Setup: Exim 4.20 on FreeBSD 4.8 forwarding mail to an internal Exchange
Server.

I would like to save a copy of emails sent to a particular address in a
particular folder based on certain keywords in the body. Say someone sends
an email to sales@ with the word quote somewhere in the body. I would like
that email to be sent on to the Exchange server, and a local copy saved to
a particular folder or passed to a script for further processing.

Any help would be appreciated,
Thanks
Kimo