Using digitally sign in email allows recipients of your emails to confirm your identity and ensure that the email you sent was not modified during transmission. Comodo's Free Email certificates allow you to use the digitally sign and encrypt features built into your personal email client such as Outlook, Thunderbird, etc to authenticate and secure your email communications.

Firstly create a Personal Secure Email Certificate from Comodo. Backup this certificate. To backup, if you are using Firefox browser, follow the instruction. After Installing Comodo certificate;

1. Open your browser (Firefox 3). Click Tools menu, then Options – Advanced – View Certificate – Your Certificate.

2. You should see your certificate there. Select this and click on Backup button to backup using any password. (See image for confirmation).

Installing and Using your Secure Email Certificate with Thunderbird (2.0.0.12)
Assigning your Certificate to your email account:

1. Open Thunderbird
2. Select Tools from and select Options from drop down menu
3. In dialog box that appears select ‘Advanced’ tab and click on the ‘View Certificates’ and click on ‘Import’ under ‘Your certificate’.

Browse to the location where you save PKCS12 file. Enter any password. Next, enter the password that you used when back up the file. Once complete the certificate will appear and you will be able to digitally sign e-mails you send out.

Encrypting and Signing a single Email: Encrypting email will only work if you have added a digitally signed email to your address book from the person you want to encrypt the email with.

1. Compose your email and attach files as usual.
2. Ensure the recipient has a Digital Certificate and you have assigned the Certificate to their entry in your contacts area (if encrypting required)
3. Choose ‘Security’ settings and click "Digitally Signing this Message" and follow the screen instructions.

Signing and Encrypting as default.
1. Open Thunderbird
2. Select Tools from menu
3. Select Account Settings from drop down menu
4. In dialog box that appears select Security tab
5. Select the appropriate certificates you wish to Sign and/or Encrypt your mails. Note that the same certificate does not have to be used for both options.