A plugin for MozillaMail that provides support for GPG/PGP signing/verification and encryption/decryption.

See http://enigmail.mozdev.org/ for downloadable .xpi files. (Note - the plugin needs to be compiled with the same major version of gcc as your mozilla - RedHat 9 and other recent distributions use gcc 3, older ones use gcc 2).

enigmail becomes a part of the mail & newsgroups application. To install the .xpi file you have to be logged in as root. You can make it by becoming su in a x-terminal and than starting mozilla in the terminal (eg. mozilla or /usr/local/mozilla/mozilla ) or you can log in as root. Off course you have to close mozilla first. Both of the methods are a security problem, because the mozilla has root-rights, so it is better just to install enigmail (or any other plug-in offered at http://www.mozdev.org) and than to close mozilla and start as a normal user without administration rights. Instructions for configuring you can find in http://enigmail.mozdev.org/configure.html. It isn't real complicated. You can make new gnupg keys with enigmail or use you own. Enigmail makes "default" keys. So if you want to have a key with 2048 kb or an alternative crypting algorithm you have to make the keys "manual" with GPG.

The only annoying feature of EnigMail for me is that there's no message filter action to pre-fetch PublicKeys when signed email arrives.--StuartYeates

See also WhySignEmail.