How does Outlook deal with temporary data encrypted with S/MIME?

Question

We are using S/MIME to encrypt messages and their attachments and Outlook as email application. All documents sent in attachment are stored on an encrypted folder and should never be copied anywhere else.

I want to know if Outlook creats a temporary file where it copies the documents before to encrypt them. If yes, how can I be sure the temporaly data have been securely deleted and cannot be retrieved by someone who has physical access to the computer?

Thanks.

Answer 1

Yes, Outlook creates temporary file in OutlookSecureTempFolder each time you're opening the attachment. You can learn more on this folder in Microsoft KB 817878. The only good way to completely secure the process of opening attachments is to specify your custom encrypted directory for OutlookSecureTempFolder registry value. You'll also be able to control its content as you wish.