S/MIME
- S/MIME in Outlook Web Access
http://technet.microsoft.com/en-us/library/aa998939(EXCHG.65).aspx - Multiple Email Client Guide
http://luxsci.com/blog/installing-smime-and-pgp-encryption-certificates-into-major-email-clients.html - GMail S/MIME Firefox Addon
https://addons.mozilla.org/en-US/firefox/addon/gmail-smime/ - Microsoft Outlook
http://support.sherweb.com/Faqs/Show/how-to-digitally-sign-and-encrypt-messages-using-smime-exchange-2010 - Old HEPKI-TAG Compatibility Chart
http://middleware.internet2.edu/hepki-tag/pki-lite/hepki-tag-pkilite-smime-clients-7.html