[exim] Need to rewrite Reply-To: and possibly Sender

I know that most view this as the wrong thing to do, but I feel I have a
decen reason why.
I have a debian sarge box running exim4 configured with
localhost.localdomain and sending to a remote smtp smarthost.
Email from it sends just fine via the phpmail module that the web site
uses.
The problem is that some external smtp servers are choking on Reply-To:
www-data@???. This is an obviously unroutable
address.
The From field is being populated correctly and the phpmail app does
specify the

I threw this into my update-exim4.conf.conf:
dc_headers_rewrite='$h_from: = $h_reply-to:'
Now I get in the header: Return-Path: <www-data@???>
This gets me half way there. Now I just need to be able replace the
www-data with the value to the left of the @.
Any ideas? I am a complete newbie to Exim and am suprised I got this
far.


Mike Gracy