DoD uses CAC as the form for logging in, authenticating and encrypting emails. I'm currently using an Apple Macbook Air with Mac OS X (Yosemite) that's enabled for CAC use. I have successfully logged in to various government DoD websites with my CAC. Successfully digitally signed and encrypted emails to several people.

However, when someone encrypt an email, my Outlook does not decrypt correctly.  Instead, the message reads "This message can't be decrypted because your private key is not valid or is missing from this computer." is seen. The same email is successfully decrypted/viewed on Apple Mail.

Under the 2011 Outlook email Account --> Advance --> Security Tab, the Digital Signature and Encryption is setup to use my CAC certificate. Is there's a setting that needs to be done for 2011 Outlook to use the CAC for decryption rather than searching through Mac OS system?