You can customize your Outlook protection settings to suit your needs. One way to protect your email is to add encryption, which helps protect mail from being read by unintended recipients, to outgoing mail.
To add protection to Outlook:
Go to the Backstage view by selecting the FILE menu (in Outlook 2007, select Tools and then select Trust Center.
In the Outlook Options dialog box, select Trust Center.
Click Trust Center Settings.
Select E-mail Security.
To add encryption to outgoing email, select the Encrypt contents and attachments for outgoing messages check box.