"Email is commonly used in business today, yet only a small percentage of users take the time to guarantee their email is sent in a secure and confidential manner. If you're not part of that elite group, read on to learn how to setup OpenPGP with the Mozilla Thunderbird mail component.
"OpenPGP is a patent-free encryption scheme based on the same security architecture as the commercial version of PGP, which has been available since the early 90's. Thunderbird uses OpenPGP through the GnuPG implementation--developed by the Free Software Foundation--for interpreting and sending digitally signed and encrypted messages..."