The Messaging and Security Feature Pack for Windows Mobile 5.0 provides native support for digitally signed, encrypted messaging. When encryption with the Secure/Multipurpose/Internet Mail Extension (S/MIME) is deployed, users can view and send S/MIME-encrypted messages from their mobile device.
The S/MIME control:
Is a standard for security enhanced e-mail messages that use a Public Key Infrastructure (PKI) to share keys