Microsoft has published guidance for IT administrators on how to restore broken Exchange Online EWS applications following the platform’s decision to block the Exchange Web Services API by default on 1 October 2026. Apps that relied on EWS, including Outlook desktop add-ins, older versions of Outlook for Windows, and Apple Mail and Calendar on macOS, have been throwing errors ranging from protocol-unavailable alerts to repeated credential prompts since the block took effect.
EWS is the API that allows applications to access Exchange mailbox data such as email, calendar entries and contacts, both from Exchange Online and on-premises Exchange Server installations. Microsoft first flagged EWS’s eventual retirement in 2018, when it announced the API would stop receiving functionality updates, and issued a formal shutdown notice in September 2023.
Two ways to re-enable EWS now
Tenant administrators who need to restore EWS access in the short term have two options. The first is to open the Microsoft 365 admin centre’s Baseline Security Mode page and uncheck “Block your entire organization from using EWS”. The second is to run Set-OrganizationConfig -EWSEnabled $true via Exchange Online PowerShell, which Microsoft says should restore access within four hours.
Microsoft is clear that this is a temporary measure, not a fix. ‘We are now in the first stage of EWS disablement, where customers are still able to re-enable EWS. Re-enabling EWS will stop working in April 2027,’ the company said. The final, permanent shutdown is scheduled for 1 April 2027, after which re-enablement will no longer be possible.
The path forward: Graph API migration
For the longer term, Microsoft is directing both administrators and developers toward migration rather than temporary re-enablement. ‘The long-term solution is to update your applications to the application versions that do not use EWS,’ Microsoft said, advising organisations to contact their application vendors for updated versions, or to recode internally built applications to remove the EWS dependency.
App developers are specifically being pointed toward the Microsoft Graph API, which Microsoft says covers most scenarios with functionality broadly equivalent to what EWS offered. Microsoft also confirmed that the retirement applies only to Microsoft 365 and Exchange Online environments; the API will continue to work in on-premises Exchange Server deployments.
Before the current block took effect, Microsoft had already trimmed the EWS surface: in October 2021 the company deprecated the 25 least-used EWS Exchange Online APIs, and support for those was removed in March 2022 on security grounds. The February 2026 announcement set out the phased disablement plan that is now under way, giving administrators until the April 2027 deadline to complete their migrations.
