UW Digital ID - Unable to decrypt messages sent from Microsoft Outlook 2010
Microsoft Outlook 2010 more fully implements standards related to the Cryptographic Message Syntax. As a result some email clients (such as Thunderbird or Apple's Mail.app) may not be able to properly decrypt messages sent from Outlook 2010.
This document details troubleshooting steps for those who are unable to decrypt messages sent from Microsoft Outlook 2010
This issue has been fixed in Microsoft Office 2010 SP1.
If you are unable to install MS Office 2010 SP1, you can use the following workaround to make Outlook 2010 revert to the behavior of earlier Outlook versions.
- Save the following file to your desktop: Outlook2010-pkifix.reg
- Right click on the file and choose "Merge"
- Exit and restart Outlook 2010
For more information see: Non-Outlook email clients unable to decrypt email sent from Outlook 2010