Microsoft Graph Subscriptions
Microsoft Graph Subscriptions let your app receive near real-time change notifications (webhooks) when Microsoft 365 data changes—such as Outlook mail and calendar items, users and groups, files in OneDrive/SharePoint, or Teams chats and channels. You register a subscription that specifies the resource to watch and a publicly reachable HTTPS endpoint; Microsoft Graph validates the endpoint and then posts notifications whenever relevant items are created, updated, or deleted.