500 votesAnonymous commented
I saw this on technet.microsoft.com
"In order to enable push notifications, the on-premises Exchange 2013 servers must connect to the Office 365 Push Notification Service to send push notifications to iPhones and iPads. Exchange 2013 on-premises servers route their update notifications through the Office 365 notification services to remove the need for enrolling developer accounts with third-party push notification services. The following diagram shows the process of how iPhone and iPad users can get badge updates for unseen messages."