ciphermail
Ciphermail email encryption gateway (S/MIME, OpenPGP, PDF encryption)
... be securely generated and stored in a tamper proof Hardware Security Module (HSM).
The built-in Data Leak Prevention (DLP) module can be used to prevent certain information to leave the organization via email.
Ciphermail can be installed on most Linux and Unix based systems. Installation packages are available for Ubuntu, Debian, Red Hat/CentOS and OpenSUSE. A ready to run virtual appliance for VMware and Hyper-V is available.