Enigmail is a plugin to Mozilla Thunderbird and Mozilla Seamonkey that allows sending and receiving of OpenPGP signed and encrypted mail. In addition, Enigmail is known to work with Eudora 8 (beta), Spicebird and Postbox.
Enigmail uses GnuPG to create OpenPGP signatures, encrypt and decrypt mail. GnuPG must be installed correctly prior to using Enigmail we provide a quick start guide and a complete set of instructions at the Enigmail Documentation web page.
You can download the latest GnuPG binaries here.