Consider the following scenario:
You receive a signed message in a Microsoft Exchange Server 2010 Service Pack 2 (SP2) environment that has Update Rollup 1 or a later update rollup installed.
The signed message contains an embedded message that has file attachments.
You open the signed message, and then open the embedded message.
In this scenario, you cannot find the attachments in the embedded message.
To resolve this issue, install the following update rollup:
2803727 Description of Update Rollup 1 for Exchange Server 2010 Service Pack 3
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.