Greylisting skipped due to bad header

Hi,

I've noticed a problem with greylisting recently where some messages are
continually temp rejected because the greylisting check is being
skipped. The affected messages _all_ seem to be legitimate NDRs from
Hotmail as far as I can tell. The reason that they are skipped is that
the "From" header has some bad characters in front of it, which causes
the greylisting code to fail (because it can't find the X-SA-Connect-IP
header).

This is what the header looks like (personal info changed):

----
Received: from [65.54.246.99] (helo=bay0-omc1-s27.bay0.hotmail.com)
  by hera.versado.net with esmtp (Exim 4.50)
  id 1HKHaa-0001C7-79
  for [email protected]; Thu, 22 Feb 2007 17:18:40 +0000
Received: from BAY124-W31 ([207.46.11.194]) by
bay0-omc1-s27.bay0.hotmail.com with Microsoft SMTPSVC(6.0.3790.2668);
   Wed, 21 Feb 2007 11:12:51 -0800
Message-ID: <[email protected]>
From: <>
Bcc:
X-OriginalArrivalTime: 21 Feb 2007 19:12:51.0089 (UTC)
FILETIME=[47EFD010:01C755EC]
Date: 21 Feb 2007 11:12:51 -0800
From: [email protected]
To: [email protected]
Date: Wed, 21 Feb 2007 11:12:50 GMT
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
  boundary="9B095B5ADSN=_49712A76E52946209FB33E26D41?WOM1.labinte"
X-DSNContext: 7ce717b1 - 1196 - 00000002 - 00000000
X-SA-Exim-Connect-IP: 65.54.246.99
X-SA-Exim-Rcpt-To: [email protected]
X-SA-Exim-Mail-From:
X-Spam-Flag: YES
----

It's really just an irritation rather that a major problem because we're
only seeing a handful of messages a week like this, and eventually the
Hotmail servers will give up, but I see them in my log reports every day
and they bug me. :)

Has anyone else seen this problem? Is there a fix/work around?

-- 
Jamie Neil | <[email protected]> | 0870 7777 454
Versado I.T. Services Ltd. | http://versado.net/ | 0845 450 1254