In an Exchange Server 2010 environment, you cannot forward a signed S/MIME message by using forwarding rules in Outlook Web App through Exchange Control Panel (ECP). Additionally, when you try to forward a signed S/MIME message, you receive the following non-delivery report (NDR):
Error Message:------------------Delivery has failed to these recipients or groups: <email@example.com>The e-mail system had a problem processing this message. Exchange will not try to redeliver this message for you. Diagnostic information for administrators: Generating server: server.contoso.com<firstname.lastname@example.org>#550 5.6.0 M2MCVT.StorageError; storage error in content conversion ##
This hotfix is scheduled to be included in Exchange Server 2010 Service Pack 1 (SP1).
In Exchange Server 2010 you can forward a signed S/MIME message in Microsoft Office Outlook or in Outlook Web App by using one of the following methods:
Forward a signed S/MIME message by using forwarding rules through ECP.
Forward a signed S/MIME message as usual.
Forward a signed S/MIME message as an attachment.
Currently, only the third method works. Therefore, we recommend that you forward a signed S/MIME message as an attachment in Microsoft Office Outlook or in Outlook Web App.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.