Paubox - Paubox provides HIPAA compliant email encryption without the hassle of extra steps.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Symantec Data Loss Prevention - Fully protect your data with the comprehensive detection technologies and unified policies of Symantec's industry leading Data Loss Prevention (DLP).
Gmvault - Backup the emails in your Gmail account.
Microsoft BitLocker - BitLocker is a full disk encryption feature included with Windows Vista and later.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X