exchange 2010 ndr issue

I have an issue and I cannot find a resolution to the problem. We use an exchange 2010 server, configured to use a smarthost, which is a smartemail server. If a mail is sent out and a NDR is generated the mail is returned to exchange and it immediately becomes a .bad mail in the replay folder, the headers before the mail is changed is

Message-ID: <634897879470655925@smtp40.hostworx.co.za>
From: "System Administrator"
To: eugene@lightfibre.co.za
Date: Thu, 29 Nov 2012 12:12:27 +0200
Subject: Delivery Failure

and after the mail is renamed to bad, it is supposed to use x-headers, but this is what the mail looks like, however notice the X-sender is missing.

x-receiver: eugene@lightfibre.co.za
Message-ID: <634897879470655925@smtp40.hostworx.co.za>
From: "System Administrator"
To: eugene@lightfibre.co.za
Date: Thu, 29 Nov 2012 12:12:27 +0200
Subject: Delivery Failure

if the header x-sender:  postmaster@lightfibre.co.za is inserted into the mail and renamed to .eml the mail gets deleivered fine to the mailbox, so it seems that microsoft takes the mail sees "system administrator" ie a null sender and fails and then re-creates the mail witout the x-sender header.

I have checked on the transport properties, to accept non deleivery and delivery reports is checked, so I am not sure how to resolve this issue.