Google recommends not to use end-to-end encryption for GMail. Why?
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Independent of whether end-to-end encryption is a good idea, independent of how much the gmail maintainers care about advertising revenue (compared to their gmail-for-businesses product): How can anyone expect them to effectively disable the core feature of their product?
Maybe it's a good idea. Or not. But it sounds a lot easier to set up your own server than to persuade the gmail developers to change the core priorities of their system.