I have outlook 2010. I have received an email from someone that I cannot open. I think it is encrypted. The mail message has a little padlock next to it. When I try to open it I get "Cannot open this item. Your Digital ID name cannot be found by the underlying security system". I have also tried to open the email on another computer also using outlook 2010 and connected to my mailbox. Same problem. When I open it in a browser based email program I get an empty email and an attached file smime.p7m (which I cannot not decrypt).
Should the email sender have sent me a key to install first? How do I open this email?