How do you password protect?

Send digitally signed and encrypted emails

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.

1. In the Mail app  on your Mac, choose File > New Message.
2. 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.
3. A Signed icon (containing a checkmark) in the message header indicates the message will be signed when you send it.
4. Address the message to recipients.
5. An Encrypt (closed lock) icon appears next to the Signed icon if your keychain contains a personal certificate for every recipient; the icon indicates the message will be encrypted when you send it.
6. If you don’t have a certificate for every recipient, you must send your message unencrypted. Click the Encrypt icon to replace the closed lock icon with an open lock icon.

Some mailing lists reject digitally signed messages because the signature is treated as an attachment. To send the message unsigned, click the Signed icon in your message; an x replaces the checkmark.

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.

Sign or encrypt emails in Mail on Mac - Apple Support