Microsoft shares how to fix broken Exchange Online EWS apps

Microsoft announced the phased retirement of the Exchange Web Services (EWS) API in Exchange Online, starting with blocking EWS by default on October 1, 2026, and final shutdown on April 1, 2027. EWS is used by various applications to access mailbox items in Exchange Online. When disabled, these apps encounter errors or repeated authentication prompts. Administrators can temporarily re-enable EWS via the Microsoft 365 admin center or Exchange Online PowerShell commands to restore app functionality. Microsoft advises developers to migrate to the Microsoft Graph API, which provides near-complete feature parity. The retirement applies only to Exchange Online and Microsoft 365; on-premises Exchange Server continues to support EWS.

Applications relying on the EWS API in Exchange Online will fail to function properly once EWS is disabled, resulting in errors and authentication prompts. This disrupts user access to mailbox data through affected apps such as older Outlook versions, Apple Mail/Calendar on macOS, and other third-party applications. The disruption impacts tenant administrators and end users until apps are updated or EWS is re-enabled temporarily. There is no indication of a security vulnerability or exploit; the impact is operational due to API deprecation.

Administrators can temporarily re-enable EWS in Exchange Online by unchecking the 'Block your entire organization from using EWS' option in the Microsoft 365 admin center Baseline Security Mode or by running the PowerShell command 'Set-OrganizationConfig -EWSEnabled $true'. This re-enables EWS within approximately four hours. However, this is a temporary measure as EWS will be permanently disabled after April 1, 2027. The long-term mitigation is to update or replace applications to use the Microsoft Graph API instead of EWS. Microsoft recommends contacting application vendors for updated versions or modifying custom applications to remove EWS dependencies.