If you want to keep messages in your Outlook information store (eg. PST-File) safe you can protect the store by using a password. However there are several tools around the net which are able to recover the the password for a PST-File.
OutLock overcomes this security leak by allowing you to encrypt (lock) sensitive messages with a single click within your Outlook information store.
OutLock encrypts the message in place. Means that the original content of a message is encrypted by OutLock and then saved to the message item. There is no additional software necessary to encrypt or decrypt the messages.