Microsoft announced today that the Exchange Web Services (EWS) API for Exchange Online will be shut down in April 2027, after nearly 20 years.

EWS is a cross-platform API for developing apps that can access Exchange mailbox items, such as email messages, meetings, and contacts, retrieved from various sources, including Exchange Online and on-premises editions of Exchange (starting with Exchange Server 2007).

Microsoft will begin blocking Exchange Online EWS by default on October 1, 2026, but administrators can temporarily maintain access via an application allowlist. The final shutdown occurs on April 1, 2027, with no exceptions granted.

Administrators who create allow lists and configure settings by the end of August 2026 will be excluded from the automatic October blocking. Starting in September 2026, Microsoft will pre-populate allow lists for organizations that have not created their own, based on each tenant’s usage patterns.

The company may also conduct temporary “scream tests” that temporarily disable EWS to expose hidden dependencies before the final cutoff, and will keep IT admins informed via monthly Message Center notifications that provide tenant-specific reminders and usage summaries.

​However, it’s important to note that this retirement process affects only Microsoft 365 and Exchange Online environments, and EWS will continue to function in on-premises Exchange Server installations.

“Today we’re announcing we will use a phased, admin controllable disablement plan that starts in October 2026 and concludes with a complete shutdown of EWS in 2027,” the Exchange Team said on Thursday. “EWS was built nearly 20 years ago, and while it served the ecosystem well, it no longer aligns with today’s security, scale, or reliability requirements.”

Microsoft also advised developers using the EWS API to switch to the Microsoft Graph API until EWS is retired, since it has reached near-complete feature parity with EWS for most scenarios.

“EWS is not being retired on-prem. Hybrid scenarios vary depending on how apps access data. On-prem mailboxes may continue using EWS; cloud mailboxes must move to Graph. Autodiscover will help apps determine mailbox location automatically,” Microsoft added.

“But note that only Exchange SE will support Graph for calls to Exchange Online, so hybrid customers will have to use Exchange SE to host on-premises mailboxes.”

Today’s announcement comes after Microsoft revealed in September 2023 that it planned to begin retiring the EWS API in October 2026, and after a 2018 warning that EWS would stop receiving functionality updates.

Three years later, in October 2021, Microsoft revealed that it had deprecated the 25 least-used EWS APIs for Exchange Online and removed support for them in March 2022 for security reasons.