@jcornutt at next weeks Zarafa Tour we will be presenting a new implemention for our WebApp to sign, encrypt and decrypt mails with S/MIME.
The Best Open Source Email & Collaboration Software
To help you understand the Zarafa architecture, a schematic presentation of Zarafa’s technical structure is shown here. When you want to install Zarafa, you can see here how the Linux server and Zarafa are integrated, as well as how Zarafa collaborates with Windows and Outlook.
There is a more extensive description of this model available in the Server manual, section 1.2.