S/MIME Encryption in Mozilla Thunderbird

If you have general questions about S/MIME encryption, you can find more information here.

In Mozilla Thunderbird, you must first import your certificate and assign it to your mail.ch account.
Certificate management in Thunderbird is handled independently of the operating system, so it does not matter whether you are using Windows, Linux, or macOS.

1. Click “Tools / Account Settings" and select your email account on the left. Then choose “S/MIME Security".

2. Click “Manage Certificates…" to open the Certificate Manager. Important: Thunderbird’s Certificate Manager corresponds to the one used in Firefox.

3. Under “Your Certificates", click “Import…" to import the previously exported .p12 file (containing your key and certificate).

4. After successfully importing the .p12 file, it will be listed under “Your Certificates". Click “OK".

5. You can now select the newly imported certificate under “Digital Signing" and “Encryption".

6. Use the checkbox to automatically sign all outgoing emails.

7. Click “OK".

8. When composing a new email, you can select under “S/MIME" whether you want to encrypt and/or sign your message.
   Depending on your selection, icons will appear in the lower right corner: the envelope for signing and the lock for encryption.
   Note that you can only send encrypted emails if you possess the recipient’s certificate.

9. Thunderbird indicates that an incoming message is signed and/or encrypted by displaying the sealed envelope and/or lock icon in the upper right corner.