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malatoi From what you are saying it is clear to me that you have NOT tried to set up your third party client with service like Protonmail or Tutanota, or you would have found out it simply does NOT work. Because of how they work, you have to use a dedicated native app to access them. And Tutanota seems to have their own push notifications implemented while Protonmail doesn't and it's unclear when it will (creators of one of the most respected privacy software bundles seem to be perfectly happy with using FCM or they would have done something about it by now).