Microsoft Previews REST-Based Exchange Online Admin API Ahead of EWS Sunset
A modern REST-based API offers IT admins a streamlined alternative as EWS approaches retirement.
Key Takeaways:
- Microsoft plans to retire Exchange Web Services (EWS) in October 2026.
- The new REST-based Admin API supports key Exchange tasks like mailbox delegation.
- Public preview is available for testing, planning migrations, and providing feedback.
Microsoft has launched a REST-based “Admin API” in public preview this week. It’s designed to help organizations move away from Exchange Web Services (EWS), which will be deprecated next year.
Microsoft plans to retire Exchange Web Services (EWS) from Exchange Online in October 2026. However, many organizations rely on EWS for certain administrative tasks. To address this gap, Microsoft introduced the Exchange Online Admin API for commercial customers.
What are the key features of the REST-based Admin API?
The Exchange Online Admin API introduces a REST-based interface that feels familiar to administrators used to PowerShell cmdlets but operates over HTTP. It focuses on a limited set of administrative tasks, such as managing organization settings, mailbox delegation, folder permissions, and group memberships. All operations use the POST method, where requests specify the cmdlet and its supported parameters for the selected endpoint.
“The Exchange Online Admin API is a REST-based administrative surface that enables a focused set of Exchange cmdlets and parameters as POST-only endpoints. The API enables access to a few key tasks that were previously available through Exchange Web Services (EWS), which is planned for deprecation in October 2026. The API is built for these specific scenarios and doesn’t replace the full Exchange administration surface in Exchange Online PowerShell,” the Exchange team explained.
To optimize performance, the API supports paging for large datasets and allows clients to select only the properties they need. It also uses routing hints via the X-AnchorMailbox header to ensure requests reach the correct backend server. The API enforces security through OAuth authentication and Exchange RBAC roles, which ensures that only authorized users can perform these tasks.
Exchange Online Admin API endpoints
The Admin API public preview introduces six endpoints that cover important Exchange Online tasks. OrganizationConfig lets IT admins view tenant-wide MailTips settings, and AcceptedDomain provides a list of accepted domains and their core configurations. Moreover, the Mailbox endpoint allows reading mailbox properties and managing “Send on behalf” delegates.
With MailboxFolderPermission, administrators can list, grant, modify, or remove permissions for folders like Inbox, Calendar, and subfolders. For group-related tasks, DistributionGroupMember retrieves membership details for distribution groups, and DynamicDistributionGroupMember does the same for dynamic distribution groups.
The new Exchange Online Admin API is currently available in public preview for commercial customers. Microsoft advises organizations to use this preview phase to test the Admin API’s capabilities, plan their migrations, and provide feedback on any missing functionality compared to existing EWS-based administrative workflows. However, there is no ETA on when this API will become generally available for all organizations.
Rabia has a master's degree in Software Engineering and she has years of experience writing professionally about Microsoft products and other technologies. Rabia has also written for OnMSFT.com as well as Windows Report. She is always up to date on t...
