Spamcop address, SMTP & OE

Per the documentation at <http://mail.spamcop.net/setup/setup_pop2.php>, I 
send outbound email thru my GMail account. I'm deliberately and with malice 
of forethought using OE at work to access my spamcop email, 
[email protected], and am reluctant to use the company email server 
for SMTP. But everyone sees my GMail address instead of my spamcop address. 
I'm hoping that this is a known problem with a straightforward solution. It 
looks like something GMail is setting for me. I'm not sure if it's the From 
or the Return-Path. I don't see where I can somehow override that in OE. A 
typical header (pardon the munging) will look like:

Microsoft Mail Internet Headers Version 2.0
Received: from wproxy.gmail.com ([64.233.184.196]) by mail.wmbpumps.com with 
Microsoft SMTPSVC(6.0.3790.1830);
  Fri, 30 Dec 2005 15:31:56 -0500
Received: by wproxy.gmail.com with SMTP id i4so1694376wra
        for <[email protected]>; Fri, 30 Dec 2005 12:31:56 -0800 (PST)
DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
        s=beta; d=gmail.com;
        h=received:message-id:reply-to:to:subject:date:mime-version:content-type:content-transfer-encoding:x-priority:x-msmail-priority:x-mailer:x-mimeole:from;
b=dudPW0iGkkEMglVk7Tc0LU43bbY3qBDCNDwgwHhQMlouMP+QS4nxeT+dr9IkUFof553feezcDlZ5bItRWWyHf9J+rwBQzB4jJSrg2souZLnyt203R3B9ZPmJyNjE2pCugvw0k3AW9FWNlfVGZmroIWQm1UHswsKmmKXq+nG3TVo=
Received: by 10.54.125.7 with SMTP id x7mr10422210wrc;
        Fri, 30 Dec 2005 12:31:56 -0800 (PST)
Return-Path: <[email protected]>
Received: from WMBLT92 ( [208.216.203.26])
        by mx.gmail.com with ESMTP id d16sm11884993wra.2005.12.30.12.31.55;
        Fri, 30 Dec 2005 12:31:56 -0800 (PST)
Message-ID: <[email protected]>
Reply-To: "Greg Stigers" <[email protected]>
To: <[email protected]>
Subject: address test
Date: Fri, 30 Dec 2005 15:31:54 -0500
MIME-Version: 1.0
Content-Type: text/plain;
 format=flowed;
 charset="iso-8859-1";
 reply-type=original
Content-Transfer-Encoding: 7bit
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.2670
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2670
From: Greg Stigers <[email protected]>
X-OriginalArrivalTime: 30 Dec 2005 20:31:56.0846 (UTC) 
FILETIME=[13F55CE0:01C60D80]

Greg Stigers