See also: E-mail | Encrypting Your Mail
Secure MIME, a popular protocol supported by a wide variety of e-mail clients and utilizing certificates. S/MIME is a Public-Key Cryptosystem and is more transparent than PGP.
TinyCA (http://tinyca.sm-zone.net/) allows the setup of a small Certificate Authority for the purposes of testing or creating S/MIME certificates
TakeDown.NET -> “S/MIME”