What is Microsoft 365 or Office 365 Push Notification Service?
From
https://learn.microsoft.com/en-us/exchange/configuring-push-...
How do I enable push notifications?
In order to enable push notifications, the on-premises Exchange 2013 servers must connect to the Microsoft 365 or Office 365 Push Notification Service to send push notifications to iPhones and iPads. Exchange 2013 on-premises servers route their update notifications through the Microsoft 365 or Office 365 notification services to remove the need for enrolling developer accounts with third-party push notification services.
So it goes like
1. Your server 2. Microsoft server 3. Apple server 4. Device
So this begs the next question: does Microsoft require warrants to disclose these notifications?