In order to use a Digital Certificate for Secure Email, you need to install the Certificate in to your specific version of Outlook and assign it to the correct profile. This is usually the default profile if you are the only one that uses your copy of Microsoft Outlook.
In most cases, when you retrieve the Digital Certificate for Secure Email, the Internet Explorer Web Browser will automatically store it in the Windows Digital Certificate Store for you. Most editions of Microsoft Outlook can automatically access the Microsoft Windows Digital Certificate Store. If for some reason the Digital Certificate for Secure Email does not properly appear visible in a version of Outlook, use the tutorials below to verify the settings.
If you used FireFox to request and retrieve your Digital Certificate for Secure Email, you may need to Export/Backup then Import/Restore the Digital Certificate for Secure Email in to Internet Explorer so that it is visible to Microsoft Windows Digital Certificate Store.
Please visit the following links for excellent tutorials on the process.
Outlook 2003
https://www.globalsign.com/support/personal-certificate/per_outlook03.html
Outlook 2007
https://www.globalsign.com/support/personal-certificate/per_outlook07.html
Outlook 2010
https://support.comodo.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1348
Outlook Express – Versions 5 and 6
http://www.comodo.com/support/products/email_certs/oe_5_6.php
Microsoft Outlook 98 – 2000
https://www.globalsign.com/support/personal-certificate/per_outlook9800.php
Windows Mobile PDA
https://www.globalsign.com/support/personal-certificate/per_wm_pda.php
In general, to Digitally Sign or Encrypt an email message, when composing the message look under the OPTIONS tab, – More Options, Security Settings, or Permissions – depending on your version of Outlook. There you will be presented with the option to Digitally Sign and/or Encrypt your message.
REMEMBER: Before you can encrypt a message to a Recipient, you must have that Recipients PUBLIC key. To exchange your key with a potential recipient, send him or her any email message that is Digitally Signed. This message will include your PUBLIC key and for future Authentication, allow the Recipient to store your key in his or her contact list. Then, the Recipient should reply back to you with his or her Public key. Once you have your intended Recipients Public Key, you can encrypt your email communications on a selective basis and vice-versa.
To learn more about Public Key and Private Key encryption read my article, “Securing your Email – Understanding Public Key and Private Key Encryption.”