Exchange Online: EWS changes affect hybrid rich coexistence and cross-org sharing
Summary
Exchange Web Services (EWS) changes in Exchange Online start between October 2026 and April 2027. Two on-premises scenarios are affected: hybrid setups with on-premises mailboxes that have online archives, and on-premises organizations with rich coexistence to a different Exchange Online organization. EWS is not deprecated on-premises.
What changes?
Free/busy, MailTips, user photos and calendar sharing between on-premises and Exchange Online can stop working if Exchange Online EWS is disabled or restricted. Hybrid rich coexistence on Exchange SE can use Graph only from the May 2026 update onwards, and on-premises mailboxes with online archives are not yet fully supported with Graph.
Affected
- Exchange hybrid organizations with on-premises mailboxes that have archive mailboxes in Exchange Online
- On-premises Exchange organizations with an organization relationship to a different Exchange Online organization (the Exchange Online tenant must keep EWS enabled)
- Not affected: hybrid organizations without on-premises mailboxes; organizations with on-premises mailboxes but no online archiving; two purely on-premises organizations
- Two Exchange Online organizations: see the Cross-Tenant Access Policy guidance from Microsoft
Preparation and temporary exceptions
- Scenario 1 (on-premises mailboxes with online archives): keep using EWS and do not yet fully switch Exchange SE servers to Graph by removing EWS permissions.
- Make sure the tenant setting EWSEnabled is TRUE.
- Add your dedicated Exchange hybrid application to the tenant's EWSAllowedAppIDs (app ID allow list).
- Scenario 2 (rich coexistence with a different Exchange Online organization): the Exchange Online organization must keep EWSEnabled set to TRUE.
Check and complete
Not fixed yet. Microsoft expects Graph support for on-premises mailboxes with online archives in the following months and is working on a solution for cross-organization sharing that does not use EWS from on-premises.
Recommendation
Check whether you run hybrid with on-premises mailboxes and online archives, or share free/busy with another Exchange Online organization. If so, verify EWSEnabled and the EWSAllowedAppIDs entry now, and update Exchange SE to at least the May 2026 update where you plan to use Graph. Do not remove EWS permissions until Microsoft supports your scenario.}],
Sources
- Impact of Exchange Online EWS Deprecation on Hybrid Rich Coexistence and Cross-org Sharing Vendor · techcommunity.microsoft.com
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, 15:55.
Where the information comes from
We continuously read the vendors’ official sources, community reports and trade media and summarise them in our own words, with a link to the source:
- Microsoft: Windows release health (Windows 10/11, Server 2016 to 2025), Windows message center, known issues of Microsoft 365 Apps (Outlook, Excel, Word, PowerPoint), Edge, Intune, Autopilot, Windows 365 and Entra Connect, Microsoft KB articles with timelines, Exchange and Windows IT Pro blogs, optionally Microsoft 365 service health and message center
- other vendors: Veeam KB, Citrix (known issues), Ubuntu and Debian (regressions), Broadcom (VMware), Fortinet, Cisco, Mozilla, Let’s Encrypt
- community (title, short excerpt and link only, without the names of the authors): Microsoft Q&A, Microsoft Tech Community (discussions), Veeam R&D Forums, Eleven Forum
- targeted web research with AI (Claude), e.g. on the updates of the month – this also finds discussions on Reddit and in forums; such entries are labelled as community reports until the vendor confirms them
- early warning from trade media (title and link only): Born’s Tech and Windows World, BleepingComputer, AskWoody, Windows Latest, Windows Central, gHacks, The Windows Club, Deskmodder, Dr. Windows, WindowsArea, Frankys Web, heise online
Summary and translation with AI (Claude by Anthropic) – without any data of visitors.
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