Enigmail is a data encryption and decryption extension for Mozilla Thunderbird and the SeaMonkey internet suite that provides OpenPGP public key e-mail encryption and signing. Enigmail works under Microsoft Windows, Unix-like, and Mac OS X operating systems. Its cryptographic functionality is handled by GNU Privacy Guard.
For S/MIME, e-mail encryption and signing, Enigmail is not needed as Thunderbird and SeaMonkey provide support for this without an extension.
Enigmail was first released in 2001 by Ramalingam Saravanan, and since 2003 maintained by Patrick Brunschwig. Both Enigmail and GNU Privacy Guard are free, open-source software.