[cliveholloway]

I would have thought a client side encryption plugin that will seamlessly encrypt/decrypt all your Gmail sent between yourself and any other user running said plugin would be a simpler option. Adding common mail suppliers as it goes forward.

[sygma]

You could use something like Mailvelope [0]. You still have to manually encrypt things, but the process is fairly straightforward.

[0]: http://www.mailvelope.com/