Over a year ago, we announced new Outlook API throttling limits on the Microsoft Graph beta endpoint. We wanted to give developers a “heads-up” that we are planning to deploy these same limits to the v1.0 endpoint (as well as the v2.0 endpoint of the Outlook REST API). This change will begin deploying on June 1, and should be fully deployed to all tenants by mid-June.

Please see Microsoft Graph throttling guidance for information on handling throttling scenarios. Or better yet, adopt our official SDKs, which handle throttling responses for you!

As a reminder, these are the new limits that will be in effect when the deployment is completed. The resources subject to these limits are documented in the Microsoft Graph throttling article.

Concurrent requests

Each application is limited to 4 concurrent requests per mailbox.

Upload limits

Each application is limited to uploading (POST, PUT, PATCH) 15 megabytes every 30 seconds per mailbox.