Digitally signing a message will apply your signature to the message. This includes your certificate (certificate: a digital method to prove the identity of a user. When sending a digitally signed message, your certificate and public key are sent together. Certificates are issued by certification bodies, and like driver's licenses, they will expire or be cancelled. ) and public key (public key: the key given by the sender to the receiver, so that the receiver can verify the sender's signature and confirm that the message has not been tampered with. The recipient also uses the public key to encrypt (lock) the e-mail sent to the sender. )。 A digital signature proves to the recipient that the content of the e-mail was signed by you, not an impostor, and that the content was not modified during transmission. Annotation encryption (encryption: the process of converting ordinary readable text into password (garbled). The sender uses the recipient's public key to encrypt (lock) e-mail messages and attachments. E-mail is an independent process. Digitally sign each email. In the message, click Options. Click Security Settings. Select the Add a digital signature to this message check box. If available, you can choose one of the following options: If you want to set up S/MIME (S/MIME: Secure Multipurpose Internet Mail Extensions (S/MIME)), which is an e-mail security specification that enables digital certificates in X.509 format and uses various encryption algorithms, such as 3DES. ) Secure recipients can read this message, please select the "Send message with clear text signature" check box. This check box is selected by default. To verify that your digital signature has been verified by the recipient, and request confirmation (the message is received without modification) and notification (telling you who opened the message and when), select the "Require S/MIME receipt of all S/MIME signed messages" check box. When sending an email with S/MIME receipt request, the confirmation information will be sent to your inbox as an email. To change other settings, such as choosing to use a specific certificate, click Change Settings. Click OK three times. Write an e-mail and send it. Tip If you use Microsoft Word as your email editor, there is a quick way to add a digital signature to your email. Open a new message, and on the E-mail toolbar, click the button. Add digital signatures to all messages In the main Microsoft Outlook window, on the Tools menu, click Options, and then click the Security tab. Select the Add a digital signature to outgoing mail check box. If available, you can choose one of the following options: If you want to set up S/MIME (S/MIME: Secure Multipurpose Internet Mail Extensions (S/MIME)), which is an e-mail security specification that enables digital certificates in X.509 format and uses various encryption algorithms, such as 3DES. ) Secure recipients can read this message, please select the "Send message with clear text signature" check box. This check box is selected by default. To verify that your digital signature has been verified by the recipient, and request confirmation (the message is received without modification) and notification (telling you who opened the message and when), select the "Require S/MIME receipt of all S/MIME signed messages" check box. When sending an email with S/MIME receipt request, the confirmation information will be sent to your inbox as an email. To change other settings, such as selecting a specific certificate to use, click Settings. Write an e-mail and send it.