Update 5/10/17: Based on feedback from our customers that the posted limit is too low for their apps, this is not currently being enforced. We're working with them and gathering data to understand what would work for their apps. We'll provide an update once we have more information.
On April 21 Exchange Online in office 365 will be enabling throttling on the outlook APIs. This will also impact apps accessing Outlook-related resources via the Microsoft Graph.
What this means: By enabling throttling on the Outlook REST APIs (accessed via
https://outlook.office365.com/api), and on the Outlook-related endpoints of the Microsoft Graph (accessed via
https://graph.microsoft.com) your app can make at most 60 requests to a single user’s mailbox in a minute.
We encourage you to review your app and determine if you are likely to exceed the limits. If so, you should look at ways to reduce the number of requests or make sure you have error handling in place to handle 429 responses and retry in an appropriate amount of time.
For more details on the API’s effected, how to track your usage, what happens if you go over your limit and how to avoid being throttled please read more here.
We will be publishing more detailed documentation on these limits in the near future.
Please let us know if you have any feedback.