Sign Email - Mozilla Thunderbird

Aug 25, 2025

Sign Email - 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.