You definitely can [0], but this one would probably be hard for google without significantly modifying the architecture of gmail in ways that would remove its revenue model. For example, they could open source a client that had audit-able end-to-end encryption, but then they couldn't optimize ad revenue by aggregating and mining large email datasets.
> a proof demonstrating that a particular problem cannot be solved as described in the claim, or that a particular set of problems cannot be solved in general
