By default, you won't be able to view any S/MIME messages on your BlackBerry. Here's how to set up your device to be able to view them.
While all communication between your device and your server is encrypted, the emails that you compose and receive end up as plain text when they're ultimately sent across the public parts of the Internet. S/MIME solves this problem by providing a way to send signed and encrypted emails across the Internet. S/MIME ensures that, in emails that are digitally signed, the sender is who she says she is, and the content wasn't altered in transit. Encrypted emails are encrypted using the recipient's public key, guaranteeing that the content can be unencrypted only by the recipient's private key.
By default, the BlackBerry can't read emails sent using S/MIME. However, if you're using a BlackBerry Enterprise Server, there is an additional software package you can purchase from RIM that allows you to send and receive S/ MIME encrypted emails. You can even wirelessly retrieve the digital certificates of users to whom you'd like to send encrypted email via an LDAP server.
When you originally installed your BlackBerry Desktop Manager, there was an optional component called Certificate Synchronization that you may or may not have installed. If you did not, you'll need to go through Add/Remove Programs in Control Panel and modify the BlackBerry Desktop Manager installation ...