The SharePoint Online Adapter/Remote Event Receiver is needed to get information about changes on watched SharePoint elements.
RemoteEventReceiver
The RemoteEventReceiver receives events from SharePoint and prepares them for further usage. Afterward, the RemoteEventReceiver sends the prepared events to the FireStart server. The RemoteEventReceiver can either be hosted locally on the FireStart server or, for example, in Azure. Azure supports SharePoint Online and SharePoint On-Premises.
SharePoint
In SharePoint, the RemoteEventReceiver is registered on every list. If an event is triggered, by creating a list entry for example, SharePoint sends the event to the RemoteEventReceiver.
FireStart Server
The SharePoint Online adapter is integrated into the FireStart server. If a new mapping is created, the RemoteEventReceiver is registered to the SharePoint list.
When the FireStart server receives an event from the RemoteEventReceiver, the server checks whether the event should be further processed or not.
