If you have a need to protect the contents of your email messages, these links should point you in the right direction.
Outlook supports the following features for cryptographic messaging: Digitally sign an e-mail message. Digital signing provides nonrepudiation and verification of contents (the message contains what the person sent, with no changes).
Encrypt an e-mail message. Encryption helps to ensure privacy by making the message unreadable to anyone other than the intended recipient.
There are additional features that can be configured for Outlook 2003 for security-enhanced messaging, if your organization chooses to provide support for them, including:
Sending an e-mail message with an S/MIME receipt request. This helps to verify that the recipient is validating your digital signature (the certificate you applied to a message).
Adding a security label to an e-mail message. Your organization can create a customized S/MIME V3 security policy which can add labels to messages. An S/MIME V3 security policy is code that you add to Outlook that runs automatically to add information to the message header about the sensitivity of the message content. For example, an Internal Use Only label might be applied to mail that should not be sent or forwarded outside of your company.