When you receive an email message in Microsoft Outlook, there is an additional attachment included with the original attachment. For example, the email message has att0001.htm or att0001.txt as an additional attachment.
This issue may occur when the following conditions are true:
The email message contains the signature of the sender and has a file attached.
The email message is sent from a mobile device that uses Microsoft Exchange ActiveSync.
This issue is currently under investigation by the mobile device manufacturer.