With reference to what i blogged earlier, i get similar queries from app developers to choose Microsoft Graph API or Outlook REST API endpoints when they develop application related to Outlook APIs.
Microsoft recommends using the Microsoft Graph API whenever possible.
- The Microsoft Graph APIs include more features than just Outlook-related APIs, including OneDrive and Active Directory.
- Both the endpoints generally provide the same functionality of Outlook REST APIs and use the same resource types.
- Choosing the Microsoft Graph endpoints allows your app to get an access token that can provide access to both Outlook data and other resources, without having to make multiple token requests.
- However, there are some features that are either only available on the Outlook endpoint, or are only in beta on the Microsoft Graph.
- If your app needs these features, you should choose the Outlook endpoints.
- For more information, please refer our detailed post regarding the same - https://docs.microsoft.com/en-us/outlook/rest/compare-graph-outlook
Hope this helps.