Gpg4win

Gpg4win is an installer package for Windows 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).

You can choose all or some of the following modules during installation:

GnuPG: The core; this is the actual encryption tool.
Kleopatra: A certificate manager for OpenPGP and X.509 (S/MIME) and common crypto dialogs.
GPA: Another certificate manager for OpenPGP and X.509 (S/MIME).
GpgOL: A plugin for Microsoft Outlook 2003 and 2007 (email encryption).
GpgEX: A plugin for Microsoft Explorer (file encryption).
Claws Mail: A complete email program including the plugin for GnuPG.
Gpg4win Compendium: The new (German!) documentation about Gpg4win2 (translation already scheduled).
Gpg4win for Novices: The old English handbook about
Gpg4win1 (for newbies).

https://www.gpg4win.org/index.html