return-path is being rewritten

hi

i've got a mail in the following form:
--zipp--
Return-Path: <maillist-bounce@foobar.cxm>
X-Original-To: locallist@mydomain.cxm
Received: from [192.168.100.99] (unknown [192.168.100.99])
by testmail (Postfix) with ESMTP id 0A0DCC78C
for <maillist-bounce@foobar.cxm>; Mon, 6 Dec 2004 17:04:31
+0100(CET)
Message-ID: <41B4832B.40600@mydomain.cxm>
Date: Mon, 06 Dec 2004 17:04:59 +0100
From: Newsletter <maillist@foobar.cxm>
User-Agent: Mozilla/5.0 (X11; U; Linux i686; de-AT; rv:1.7.3) Gecko/20041004
X-Accept-Language: de, de-de, en-us, en
MIME-Version: 1.0
To: locallist@mydomain.cxm
Subject: this is a test
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-Envelope-From: maillist@foobar.cxm

Hello,

this is a test.

bye
--zapp--


as you can see "From:" and "Return-Path:" differ.
because i want to send this email to numerous recipients
(procmail will do this later)
i tried to use
--zipp--
cat mail | sendmail -t
--zapp--
but then postfix sets "Return-Path" to root@local.server.cxm

whenn i use
--zipp--
cat mail | sendmail -t -f maillist@foobar.cxm
--zapp--
postfix sets "From:" as well as "Return-Path" to give address

So how do I prevent postfix from rewriting the "Return-Path"?
Or how do i set it manually?

--
Best regards,
Bjoern Kaiser NOSPAM-bjoern-at-kyza.de