Intermittently receiving blank emails from one company

We have been Intermittently receiving blank emails from one company.  The subject comes through ok, but the body will be blank.  If we reply letting them know it was blank and they resend it has always comes through.  They are using GroupWise (maybe 6.5.7 judging by the header?) and we're using Exchange 2003 SP2.  The issue is intermittent, and we are able to receive HTML emails in testing.  I don't have much to go on other than that comparing the headers of an intentionally blank email and one of the unintentionally blank emails it seems that transmission of the unintentionally blank email was interrupted or truncated.  Has anyone else experienced this?  Can you give me some direction in debugging?  The headers are below.

-----------------Intentionally Blank Message Header-----------------
Microsoft Mail Internet Headers Version 2.0
Received: from sender.com ([xxx.xxx.xxx.xxx]) by mail.recipient.com with Microsoft SMTPSVC(6.0.3790.1830);
       Thu, 21 Jun 2007 17:02:40 -0400
Received: from sender_Dom-MTA by sender.com
      with Novell_GroupWise; Thu, 21 Jun 2007 17:00:10 -0400
Message-Id: <s67aae9a.096@sender.com>
X-Mailer: Novell GroupWise Internet Agent 6.5.7
Date: Thu, 21 Jun 2007 16:59:40 -0400
From: "John Doe" <John.Doe@sender.com>
To: <JDoe@recipient.com>
Subject: HTML email, no message body
Return-Path: John.Doe@sender.com
X-OriginalArrivalTime: 21 Jun 2007 21:02:40.0921 (UTC) FILETIME=[815A6090:01C7B447]

-----------------Unintentionally Blank Message Header-----------------
Microsoft Mail Internet Headers Version 2.0
Received: from sender.com ([xxx.xxx.xxx.xxx]) by mail.recipient.com with Microsoft SMTPSVC(6.0.3790.1830);
       Thu, 21 Jun 2007 12:17:28 -0400
Received: from sender_Dom-MTA by sender.com
      with Novell_GroupWise; Thu, 21 Jun 2007 12:14:59 -0400
Message-Id: <s67a6bc3.085@sender.com>
X-Mailer: Novell GroupWise Internet Agent 6.5.7
Date: Thu, 21 Jun 2007 12:14:20 -0400
From: "John Doe" <John.Doe@sender.com>
To: "John Doe" <JDoe@recipient.com>
Subject: Re: FW: Parking Garage
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="=__Part3B1C0ACC.0__="
Return-Path: John.Doe@sender.com
X-OriginalArrivalTime: 21 Jun 2007 16:17:29.0951 (UTC) FILETIME=[AA6B8EF0:01C7B41F]

--=__Part3B1C0ACC.0__=
Content-Type: text/plain; charset=
Start Free Trial