Consider the following scenario. A MIME-encoded message that includes an inline attachment arrives in Microsoft Exchange Server. You try to access the message from a Microsoft Outlook 2010 or Microsoft Office Outlook 2007 client. In this scenario, the attachment is hidden, and it is unavailable for download. If you use Microsoft Office Outlook Web Access to view the same message, the inline attachment is still hidden. However, the inline attachment is available for download in Outlook Web Access, and you can click the message and view it.
This issue occurs when Exchange Server does not validate whether there is a reference to the inline attachment. If the inline attachment is not referenced, the inline attachment is hidden.
Exchange Server 2010
Stop the Exchange Transport service.
Locate the EdgeTransport.exe.config file. This file is located in the following path: