True, email requires more players to stay federated and would have reflected well with Mozilla's supposed ethos. But, I seriously doubt whether Mozilla would have pulled off what Hey did in terms of marketing.
Mozilla's marketing for the hypothetical email service would have been like ProtonMail without the advantage of 'Switzerland/CERN' brand. Also, ProtonMail has now gone all guns on Apple following Hey, which I don't think Mozilla would do.
While Mozilla would likely not go head on against Apple, Mozilla still have some aura especially in the Silicon Valley. Who knows, they might have cut a deal with Apple...
