Digitally Sign Emails – Mozilla Thunderbird

1:: Open a new email window in Mozilla Thunderbird. Go to Tools > Account Settings.

2:: Click the Security tab. Click Select next to the Digital Signing field.

3:: Choose the certificate you intend to use for signing. Click OK.

Note: If no certificates are present, it still needs to be imported. Follow these instructions and then return to this article to continue.

4:: You can choose the encryption certificate here as well:

5:: To sign all messages, check Digitally sign messages (by default) under the Digital Signing field:

6:: Click OK to complete. 
If you are not signing by default, proceed to the next step for instructions on signing a single email.

7:: When composing a new email in Thunderbird, click the Security drop down menu and choose Digitally Sign This Message.

Note: To send encrypted messages, you must first receive a digitally signed email message from the recipient.