What changed
Cross-tenant free/busy, MailTips and calendar sharing between two Microsoft 365 organizations used to run over EWS, set up through Organization Relationships or Sharing Policies. Microsoft began disabling EWS in Exchange Online on October 1, 2026. As that reaches a tenant, those cross-organization lookups stop working until both organizations move to the replacement, Microsoft 365 Cross-Tenant Access Policy. Admins can switch EWS back on temporarily, but it’s disabled for good from April 1, 2027. Hybrid and on-premises setups aren’t affected by this change.
When you can’t get both IT teams to fix it
The proper fix needs the admins of both organizations. If you’re one person working across two organizations, such as a consultant or contractor with a client account, that can be hard to arrange. Kelbra takes a different route: you connect each of your own calendars with your own sign-in, through Microsoft Graph rather than EWS, and Kelbra copies your events between them, as plain "Busy" blocks if you prefer. People in each organization then see your real availability in your calendar there, with no federation setup between the companies.
What to do
Confirm it’s EWS. If cross-organization free/busy or a shared calendar from another Microsoft 365 company stopped working in October 2026, while everything inside your own organization still works, this change is the most likely cause.
Ask your Microsoft 365 admin to check whether your organization shares free/busy or calendars with other tenants through Organization Relationships or Sharing Policies. Microsoft’s message center post MC1446796 explains how to assess this and links to the migration guide.
The lasting fix: the admins of both organizations set up Microsoft 365 Cross-Tenant Access Policy. Free/busy is available there now; cross-tenant calendar sharing arrives in mid-October 2026.
For breathing room, an admin can temporarily turn EWS back on for the tenant. That only lasts until April 1, 2027, so use the time to migrate.
If you’re an individual with accounts in more than one organization and can’t get both IT teams involved, connect each calendar to Kelbra instead. Your tenant may require an admin to approve third-party apps first; Kelbra shows a clear message if the connection is blocked for that reason.
Questions
Why can’t people at another company see my free/busy anymore?
Free/busy between two Microsoft 365 organizations ran over Exchange Web Services, which Microsoft started disabling on October 1, 2026. Until both organizations move to Microsoft 365 Cross-Tenant Access Policy, those lookups can stop working.
When does EWS stop working completely?
Microsoft began disabling EWS in Exchange Online on October 1, 2026. Admins can temporarily re-enable it, but it is disabled permanently from April 1, 2027.
Does this affect calendars inside my own organization?
No. This change is about sharing between separate Microsoft 365 organizations. Hybrid and on-premises Exchange setups are also out of scope.
Is Kelbra affected by the EWS retirement?
No. Kelbra connects to Outlook through Microsoft Graph, using your own sign-in for each account, not EWS.
Is Kelbra the same as cross-tenant free/busy?
Not quite. Cross-tenant free/busy lets people look up your availability in another organization. Kelbra instead copies your events between your own calendars, as full details or as "Busy" blocks, so each calendar already shows your real availability. It works for you personally rather than for a whole organization.