Weird EV messages with blank subject for some users

Hi,

we have some users who use Apple Mail with EV and they get strange (nearly) blank messages, with a blank subject line, every few days:

Subject: 

Date: December 23, 2008 3:00:10 PM PST 

Message-Id: <D325F772BEACFA4CAAD087712918FCD9018AF13443@EX01.YOUGOV.local<mailto:D325F772BEACFA4CAAD087712918FCD9018AF13443@EX01.YOUGOV.local>>

Accept-Language: en-US, de-DE 

Content-Language: en-US 

X-Ms-Has-Attach: yes 

X-Ms-Tnef-Correlator: 

Content-Type: multipart/mixed; boundary="_002_D325F772BEACFA4CAAD087712918FCD9018AF13443EX01YOUGOVloc_" 

Mime-Version: 1.0 

Attached to this is a text file with this included:

Subject: Date: December 23, 2008 3:00:10 PM PST Message-Id: <D325F772BEACFA4CAAD087712918FCD9018AF13443@EX01.YOUGOV.local<mailto:D325F772BEACFA4CAAD087712918FCD9018AF13443@EX01.YOUGOV.local>> Accept-Language: en-US, de-DE Content-Language: en-US X-Ms-Has-Attach: yes X-Ms-Tnef-Correlator: Content-Type: multipart/mixed; boundary="_002_D325F772BEACFA4CAAD087712918FCD9018AF13443EX01YOUGOVloc_" Mime-Version: 1.0

Does anyone know what this is, why these only seem to appear in Apple Mail (not in Outlook) and how to get rid of it?

Thanks for any help!