Enigmail (composed of the words Enigma and e-mail ) is an extension for Mozilla Thunderbird and the mail News of SeaMonkey for signing and encrypting electronic messages and attached files using the OpenPGP standard. It is seamlessly integrated into the graphical user interface of these programs. The cryptographic functions ( encrypt, decrypt, sign and verify ) are not executed by the module itself, but passed in the background to GnuPG, which must be available to the system as well. In addition to running GnuPG operations Enigmail can also perform even some OpenPGP functions, such as searching for missing keys. Enigmail supports PGP / INLINE ( according to RFC 2440 ) and PGP / MIME ( RFC 3156 ).

Besides OpenPGP still exists another standard for signing or encrypting e -mails, namely S / MIME. For this purpose, Mozilla already offers native support, so that Thunderbird needs any additional extensions.