As shared in Exchange Online EWS, Your Time is Almost Up, Exchange Web Services in Exchange Online will begin phased disablement in October 2026 and will be fully disabled in April 2027. As part of this work, we are addressing the remaining Exchange Server collaboration scenarios that currently depend on the Exchange Online EWS endpoint.
Most Exchange Server Free/Busy scenarios will not change. Free/Busy between two Exchange Server (purely on-premises) organizations will continue using Federation/DAuth and Organization Relationships. Exchange hybrid organization can continue sharing Free/Busy between Exchange Server and its own Exchange Online tenant using OAuth and IntraOrganizationConnectors through the dedicated Exchange hybrid app, with Graph replacing EWS in the modern hybrid flow.
The scenario requiring a new path is an Exchange Server organization retrieving Free/Busy or MailTips from another organization’s Exchange Online tenant through an EWS-dependent Organization Relationship. For Exchange Server to external Exchange Online scenario, we are evaluating leveraging Microsoft 365 Cross-Tenant Access Policy which is also becoming the standard for Free/Busy, calendar, and MailTips collaboration between Microsoft 365 tenants.
Before finalizing the direction, we want feedback from customers and partners – particularly organizations that operate Exchange Server without an existing M365 tenant.
Please share your feedback on this approach through the form: Survey
This feedback request is specifically about Exchange Server (Organization A) to a different Exchange Online (Organization B) collaboration. Exchange Server-to-Exchange Server Organization Relationships (two purely on-premises organizations) are not in scope and will continue unchanged.
The Exchange Team