Exchange Online: EWS deprecation needs EWSAllowedAppIDs, Microsoft disables EWS in some tenants

Summary

Microsoft has started deprecating Exchange Web Services (EWS) in Exchange Online. In the multi-tenant (WW) cloud, EWSEnabled = True alone no longer keeps EWS working; an app ID allow list (EWSAllowedAppIDs) is required. Microsoft is disabling EWS in tenants where both settings are empty. Tenants already set to EWSEnabled = True are not changed until April 2027.

What changes?

Applications and add-ins that use EWS stop working once EWS is disabled in the tenant or if their AppID is not in EWSAllowedAppIDs. Microsoft clients such as Classic Outlook for Mac and Excel Power Query may be affected.

Affected

• Exchange Online tenants in the multi-tenant (WW) cloud
• Tenants with EWSEnabled empty (Null) and EWSAllowedAppIDs empty: 7-day Message Center warning, then EWS disabled
• Tenants with EWSEnabled = True set after October 11: admin must populate EWSAllowedAppIDs
• Apps in the EWS usage report: Outlook for Windows (older than build 16.0.20430.20092), Classic Outlook for Mac, Excel Power Query, PowerBI, Exchange hybrid
• Sovereign clouds: timeline follows later

Preparation and temporary exceptions

1. Review the EWS usage report and identify apps that still use EWS.
2. Add the AppIDs of the required apps to EWSAllowedAppIDs (takes 24 hours to apply).
3. If Microsoft has disabled EWS, the tenant admin can temporarily re-enable it by setting EWSEnabled (usually under 1 hour, up to 4 hours) as described in the Microsoft article "Exchange Online EWS application stopped working? Do this".
4. For Classic Outlook for Mac, add the "Microsoft Office" AppID to EWSAllowedAppIDs, or switch to new Outlook for Mac.
5. The EWSAllowList property is unrelated and needs no change.

Check and complete

Not a defect; this is a planned retirement. Microsoft will not change EWS availability for tenants already set to EWSEnabled = True until April 2027.

Recommendation

Check the EWS usage report and Message Center now. Update Outlook for Windows to build 16.0.20430.20092 or higher, move Mac users to new Outlook, and review third-party and line-of-business apps that use EWS. Add only required AppIDs to EWSAllowedAppIDs and plan the migration to Microsoft Graph or other supported APIs before April 2027.

Timeline

1. 10 Oct 2026Microsoft populated EWSAllowedAppIDs for all multi-tenant (WW) tenants with EWSEnabled = True and an empty list (October 10-11).
2. 26 Oct 2026EWS deprecation in Exchange Online starts. Tenants with EWSEnabled and EWSAllowedAppIDs both empty get a 7-day Message Center warning, then Microsoft populates the list (based on 60-day usage) and sets EWSEnabled = False.

Sources

• EWS Deprecation Is Here – What This Means To You (Exchange Team Blog) Vendor · techcommunity.microsoft.com
• Excel Power Query EWS retirement News · aka.ms

Compiled from the sources listed and translated with AI (Claude); status and dates come from the vendor. The vendor’s statements are authoritative. Updated 1 Nov 2026, 15:37.