Importing a pfx file into Thunderbird
The Thunderbird recipient receives the following message1 containing an attached password encrypted pfx:
1. Save the pfx attachment onto your system
2. Open the certificates options page
Open tools menu Tools → options, select the Advanced settings and open the Certificates tab
3. Click "View Certificates"
This opens the "Certificate Manager" dialog
4. Click "Import" and select the pfx from step 1.
The first time you add a certificate you are asked to set a "Master Password". The master password is used to protect the private keys stored in Thunderbird. The private keys are encrypted with the master password to ensure that only you can access the private keys. You only have to set the master password once.
Note: this is NOT the password for the pfx file that has been handed out to you! The master password should be chosen by you.
5. Set the master password and click "OK"
6. Enter the pfx password and click "OK"
you are now asked for the password of the password protected pfx file. This is the password that was given to you via SMS Text message or in some other way.
7. Finished.
Now that you have installed a certificate and private key you are able to receive encrypted email.
[The following steps are only required if you want to send encrypted email]
Trust the imported certificate
The certificate with the private key and the root and intermediate certificates have now been installed. You should now manually trust the root certificate because it is not automatically trusted. You first need to find out which root you need to trust.1. Open "Your Certificates" tab on the "Certificate Manager"
Open tools menu Tools → options, select the Advanced settings and open the Certificates tab, Click "View Certificates" and select the "Your Certificates" tab.
2. View certificate properties and get the name of the root
Double-click the certificate you just installed. The certificate details should now be opened. The first entry in the "Certificate Hierarchy" is the root certificate. You should remember the name of the root certificate because you will need it in the next steps.
3. Select the root certificate
Open the "Certificate Manager" (see step 1) and select the "Authorities" tab. In the certificate list select the root certificate from step 2.
4. Trust the root certificate
Click the "Edit" button and select "This certificate can identify mail users.".
Associate the certificate with your account
The imported certificate must be associated with your email account.1. Open the security settings for your Tunderbird account
Open Tools → Account settings... and select the "Security" options for your account.
2. Select the signing certificate
Click "Select..." for the "Digital Signing" certificate and select the certificate you just imported.3. Select the encryption certificate
Click "Select..." for the "Encryption" certificate and select the certificate you just imported.4. Finish.
We will now explain how to receive and send encrypted email.
Receiving signed and encrypted email
A signed and encrypted message looks as follows:
The 'lock' 
shows that the message was encrypted and the 'envelope'
shows that the message was signed.
Sending signed and encrypted email
1. Enable encryption and signing
Enable "Encrypt This Message" and "Digitally Sign This Message" from the security menu.