A digitally signed message lets your recipients verify your identity as the sender; an encrypted message offers an even higher level of security. To send signed messages, you must have a personal certificate in your keychain. To send encrypted messages, the recipient’s certificate must be in your keychain.
In the Mail app
on your Mac, choose File> New Message.Move the pointer over the From field, click the pop-up menu that appears, then choose the account for which you have a personal certificate in your keychain.
A signed icon (containing a checkmark) is shown in the message header and indicates your message will be signed when you send it.
Address the message to recipients.
An encrypted icon (containing a closed lock) is shown if your keychain contains a personal certificate for every recipient. If you don’t have a certificate for every recipient, click the encrypted icon in your message; an open lock replaces the closed lock, indicating the message will be sent unencrypted.
on your Mac, choose File> New Message.Some mailing lists reject digitally signed messages because the signature is treated as an attachment. If this happens, click the signed icon in your message; an x replaces the checkmark, indicating the message will be sent unsigned.
Note: If for some reason your certificate isn’t associated with your email address, or if you want to use your certificate with a different email address, Control-click the certificate in Keychain Access, choose New Identity Preference, and provide the requested information.
