Just read a useful article on lxer.com titled how to back up and restore gmail account in linux: http://xmodulo.com/2013/08/how-to-back-up-and-restore-gmail-account-on-linux.html

It makes use of “Gmvault” to make a complete backup of your gmail account on your own computer.

Seems like a useful application but might take a while if you’re backing up a few GB over the internet.