Outlook

Use Digital IDs (Certificates) to prove your identity in Outlook email transactions

See MVP Manu Philip‘s article on Outlook 2010 posted on MVP Award Program Blog – MVP Monday Series. http://blogs.msdn.com/b/mvpawardprogram/archive/2012/04/09/use-digital-ids-certificates-to-prove-your-identity-in-outlook-email-transactions.aspx