I am evaluating using Mattermost for internal corporate chat. This includes potentially using the Mattermost Push Notifications Service to push notifications to corporate iPhones. Mattermost says:
For organizations who want to keep internal communications behind their firewall, this service encrypts notification messages with a private key under your control before sending them to Apple's public push notification service for delivery to your iOS devices.
Implementing a push notification service to push notifications to iPhones is new to me. I have seen other posts about the reliability and privacy of the APNS, but are there any options for sending notifications through a service that doesn't have to go through Apple? If the answer is no, the implication is that all notifications for the 1B+ iPhones on the planet go through Apple...correct? Again this is new to me so I am just trying to clarify my understanding of the overall architecture.