Technichor has introduced Horcrux Email Backup (http://thehorcrux.com/), a Mac app that lets email users automatically keep their data rather than surrendering it to third party services.
Horcrux takes daily snapshots of email accounts. The app is continuous and in real time, so that as soon as a new email is added it will be transferred. It gives users the option to change email providers without losing prior data. Horcrux will also migrate the emails to another email service.
Horcrux Email Backup requires Mac OS X 10.7 or higher. It costs US$14.99 and is available at the Mac App Store in the Utilities category.