The Exchange server provides message notifications to Email Notification Service (ENS) by either streaming the notifications or pushing the notifications. These message notification mechanisms determine how ENS and the Exchange server interact with each other.
After the Email Notification Service (ENS) fetches the device and user details from AirWatch, it subscribes these device users to the Exchange endpoint through the Exchange Web Service (EWS). To subscribe these device users, ENS uses a service account with an impersonation role assigned to it. This subscription creates a connection between the ENS and Exchange server.
Whether the connection established between the ENS and the Exchange server is an open connection or not depends on the notification mechanism chosen while installing the ENS.
After ENS subscribes the users to the Exchange server, a connection is created between the Exchange and the ENS server. This connection remains open for a specified period to allow the Exchange to stream the notifications to the ENS server. In this kind of mechanism, ENS does not have to poll the Exchange server for pending notifications.
For push notifications, there is no open connection created between the ENS and the Exchange server after ENS subscribes the users to the Exchange. For a new message, Exchange pushes the message event to ENS and ENS then fetches the mail details from the Exchange. Exchange provides near real-time notifications and therefore polling of the Exchange server is not required.