FreeEncrypt for Outlook is Freeware, you can use it for free, no registration is required. It is a easiest and quickliest encrypting e-mail tool, It provides tight integration with the Microsoft Outlook 2000 or later, supports creation of the encryption rules for e-mail message, this helps to automatically encrypt/decrypt the email message. FreeEncrypt for Outlook cryptographic algorithm is similar to Vigenere. This is a famous and quick cryptographic algorithm.
More info:
hxxp://www.encryptgenie.com/