As the aforementioned tutorial may be outdated or technikal skill required may be to much for everyday user and as this days the email security is a must, here I'll present a new, free way to acquire and use a digital certificate for your email.
The free certificate will be acquired from Comodo and used in Thunderbird email client.
|Sign and encrypt your emails using Thunderbird and Comodo Certificates|
Step 1: Sign up for a Comodo Free Email certificateAccess https://www.comodo.com/home/email-security/free-email-certificate.php and follow the instructions. Important to known: use the Firefox Browser for that and keep it open after that. and, of course, use your real email address in the sign up form.
After a successfully application, instructions on how to collect the certificate will arrive on the email address provided.
Step 2: Open the email arrived from ComodoIn this email you will see a red button "Click & Install Comodo Email Certificate". Don't click on it, but instead right click this button and select "Copy Link Address".
Return to Firefox Browser, open a new tab (Ctr+T) and paste the copied address. A confirmation message should inform that the certificate have been installed.
Step 3: Save the certificate from Firefox to a known locationTo do that, access Firefox->Preferences->Privacy & security ->View Certificates -> Your certificates
Select the fresh one just acquired and then Backup.
Step 4: Import the certificate in ThunderbirdOpen Thunderbird, right click on your email account, settings->security->manage certificates.
Select Your certificates tab then Import the above backup-ed certificate.