You can also set your email program to encrypt all of you emails under Tools/Options.
To encrypt emails, however, first you have to get a Digital ID. Digital IDs are a special type of security document that helps to validate your identity. They can be used to sign or encrypt important documents electronically. The Digital ID has two parts: a private part that only you use and a public key. The private key must be kept securely, preferably on a secure device like a smart card. The public is made available to all.
For example, if you wish to send an e-mail securely, you will encrypt your message with your recipient's public key. Upon receiving the e-mail, your intended recipient will use his/her private key to unscramble the communication. As only your intended recipient has access to his/her private key, no one else should be able to read the content of your email. Conversely, if your intended recipient wants to sign a communication, he/she will generate a unique signature with his/her private key. Anyone in possession of his/her public key will be able to verify that the message was written by him/her.
The Digital ID is also sometimes called a digital certificate, and this type of two-part Digital ID security, with both private and public parts to the ID, is known as public key cryptography.
To learn where to get your Digital ID for use with Microsoft Office as well as other programs visit the link below. (See also, How private are my emails?)
For more information, visite the Microsoft office website