What happens for people that never log in to Gmail through a browser but only download their email? Are they supposed to be prevented from downloading the DRMed messages? They must be if this 'security' method is going to do what it claims because otherwise anyone can download the message and then use an alternate mail client to do as they wish.
Also how is this DRM supposed to work? I doubt Google is getting involved since there's been no huge demand for such a feature so the company has to be taking advantage of how Gmail works. Perhaps they are inserting a bit of code into the email that prevents you from selecting certain options. Nothing unsafe in having email that changes how the email client behaves, is there?