gpg4o!

Gpg4win is an installer package for Windows (2000/XP/2003/Vista) with computer programs and handbooks for email and file encryption. Both relevant cryptography standards are supported, OpenPGP and S/MIME. Gpg4win and the software included with Gpg4win are Free Software (among other things free of charge for all commercial and non-commercial purposes).

Outlook Privacy Plugin is a security extension for Outlook 2010. It enables Outlook 2010 to send and receive email messages that are encrypted and/or signed with the OpenPGP standard.