Microsoft has confirmed that it will retire the Exchange Web Services, or EWS, API for Exchange Online in April 2027. It will mark the end of a service that has been in use for nearly 20 years.
EWS is a cross-platform API that allows apps to access Exchange mailbox data. This includes emails, calendar events, contacts, and other mailbox items. It has been widely used by enterprise apps, email tools, and integrations that work with Microsoft 365 and Exchange Online.
Microsoft says the shutdown will follow a phased approach. Starting October 1, 2026, EWS access will be blocked by default for Exchange Online. Administrators will still be able to allow access temporarily using an application allowlist. The final shutdown will happen on April 1, 2027, and no exceptions will be allowed after that date.
Organizations that create allowlists and configure their settings by the end of August 2026 will avoid the automatic blocking in October. For tenants that do not take action, Microsoft will begin pre-populating allowlists in September 2026 based on how EWS is currently used in each environment.
Microsoft has also warned that it may run short-term “scream tests” before the final shutdown. These tests will temporarily disable EWS to help organizations identify hidden dependencies. IT administrators will receive regular reminders and usage summaries through the Microsoft 365 Message Center.
The retirement only affects Exchange Online and Microsoft 365. EWS will continue to work in on-premises Exchange Server deployments. However, hybrid environments will need special attention. Apps accessing cloud mailboxes must move to Microsoft Graph, while on-prem mailboxes can continue using EWS. Microsoft says Autodiscover will help apps detect mailbox location automatically.
Microsoft is urging developers to migrate to the Microsoft Graph API as soon as possible. The company says Graph has reached near-complete feature parity with EWS for most use cases and better aligns with modern security and reliability requirements.
For hybrid customers, Microsoft noted that only the Exchange Server Subscription Edition will support Graph calls to Exchange Online. This means organizations running hybrid setups may need to upgrade their on-prem Exchange servers.
The announcement is not entirely new. Microsoft first revealed plans to retire EWS in September 2023 and had already stopped adding new features to the API back in 2018. In 2021, Microsoft deprecated several low-usage EWS APIs and fully removed support for them in 2022 due to security concerns.
