Filtering problem (Envelope-to:)

Hello,

I am having problems filtering mailing list mail that arrives with no
To: header, but instead an Envelope-to: header. (Simply filtering
on From: is not an option in my case.) The problem is that
$header_Envelope-to: never gets a value. I created a test message
that looked like this:

From: lipsitz@???
Envelope-to: radlow@???
Subject: Free Magazines!

etc...

and a test .forward:

   # Exim filter    <= do not remove this line
   testprint $header_Envelope-to:
   if $header_Envelope-to: matches "(.*)@trefoil.com" then
      deliver radlow@???
   endif

and used sendmail -bf .test-forward < foo. Doesn't deliver the
mail. :)

Is there a way to get at the Envelope-to header?

Thanks,

Jeremy Radlow
radlow@???