In Octoboer 2017, we published a blog notifying our developer community of our plan to deprecate the Outlook REST API v1.0. 

Today we are announcing that on April 30, 2021, we will fully deprecate the Outlook REST API v1.0 endpoint. 

After this date, applications can no longer call the Outlook Rest API v1.0. If your applications are currently using Outlook REST API v1.0, you should plan to transition to Microsoft Graph to ensure continued access to Exchange Online data. 

Please note that we also recently announced the deprecation of Outlook REST API v2.0. That announcement, in addition to this update, are indicators of our commitment to migrating our app ecosystem to the modern Microsoft Graph. 

For more information and details about how to plan for your app’s transition from the Outlook REST API v1.0, see: 

• Getting started with Microsoft Graph using OAuth2 
• Transitioning from Outlook v1.0 to Microsoft Graph 

Thanks for continuing with us on our journey as we work to improve productivity for everyone on the planet, and please let us know if you have any additional questions or concerns by reaching out to our Q&A Mail forum.