MC1446796 - Migrate Free/Busy, MailTips, and Calendar Sharing before EWS deprecation

What and Why:

Exchange Web Services (EWS) deprecation begins October 1, 2026. Cross-tenant collaboration features — Free/Busy, MailTips, and Calendar Sharing — currently rely on EWS.

Cross-tenant Free/Busy, MailTips, and Calendar Sharing via Microsoft 365 Cross-Tenant Access Policy, which replaces EWS-based cross-tenant collaboration, will be available starting September 2026.

Rollout Schedule:

• Worldwide: We will begin rolling out in August 2026 and expect to complete by September 1, 2026.
• GCC: We will begin rolling out mid-August 2026 and expect to complete by mid-September 2026.
• GCC High: We will begin rolling out early September 2026 and expect to complete by end of September 2026.
• DoD: We will begin rolling out early September 2026 and expect to complete by end of September 2026.

Impact on your organization:

Sharing Free/Busy, Calendars, and MailTips (e.g., out of office message) with another Microsoft 365 organization via Organization Relationship, Availability Address Space, or Sharing Policy relies on Exchange Web Services (EWS), which is being deprecated. To preserve these cross-tenant collaboration scenarios, you will need to start migrating to Microsoft 365 Cross Tenant Access Policy.

Your tenant is affected if it uses any of the following Exchange Online configurations:

• Organization Relationships — sharing Free/Busy or MailTips with other Microsoft 365 tenants 
• Availability Address Spaces — sharing Free/Busy with other Microsoft 365 tenants (AccessMethod: OrgWideFBToken) 
• Sharing Policies — sharing calendars externally, either via invitations sent to recipients in other Microsoft 365 organizations or calendars published for anonymous access via an internet URL

Run these commands in Exchange Online PowerShell to check if your tenant is affected: 

• Get-OrganizationRelationship | Format-List Name, DomainNames, Enabled, FreeBusyAccessEnabled, FreeBusyAccessLevel, FreeBusyAccessScope, MailTipsAccessEnabled, MailTipsAccessLevel, MailTipsAccessScope
  • If results show (1) Enabled: True, and (2) either FreeBusyAccessEnabled: True or MailtipsAccessEnabled: True, and (3) the external organization is hosted in Microsoft 365, your tenant is affected and in scope to migrate. Else, no action is needed. 
• Get-AvailabilityAddressSpace | Format-List ForestName, AccessMethod 
  • If results show (1) AccessMethod: OrgWideFBToken, and (2) the external organization is hosted in Microsoft 365, your tenant is affected and in scope to migrate. Else, no action is needed. 
• Get-SharingPolicy | Format-List Name, Domains, Enabled, Default
  • If results show (1) Enabled: True, and (2) the Domains property contains at least one rule with a CalendarSharingFreeBusy access level (Simple, Detail, or Reviewer), and (3) the targeted external organization is hosted in Microsoft 365, and (4) the policy is assigned to one or more mailboxes, your tenant is affected and in scope to migrate. Else, no action is needed.
  • Note: rules that begin with Anonymous: represent calendar publishing to anonymous internet recipients via a published URL - these also appear in this output.

What happens if I do nothing:

Starting October 1, 2026, Exchange Web Services (EWS) will be gradually disabled in line with previous communications linked to this message. As this rollout reaches your tenant, cross-tenant Free/Busy, MailTips, and Calendar Sharing that rely on EWS will be affected — recipients in partner organizations may no longer see Free/Busy, MailTips, or shared calendars from your tenant. 

If your organization is not ready to migrate, you can retain EWS access by following the guidance of the latest blog we published: ExchangeOnline EWS, Your Time is Almost Up (EWSEnabled set to True) while you prepare and execute the migration steps attached to this message. EWS access through this extension will remain available until the final EWS shutdown on April 1, 2027. 

Action Required/Recommendations:

• Follow the Roadmap post for updates to the rollout schedule. To avoid impact, plan to migrate after the rollout reaches your tenant and before EWS deprecation.
• Review the migration guide linked below for step-by-step instructions to understand your current configurations, set up new Microsoft 365 Cross Tenant Access Policies, validate the new configurations, and remove unused configurations. 
• Hybrid and on-premises scenarios are not in scope. This update applies to fully cloud-hosted (Exchange Online ↔ Exchange Online) cross-tenant and cross-cloud configurations only. For organizations running on-premises Exchange and Exchange Online in a Hybrid Deployment, migrate to Dedicated Hybrid App. For organizations hosted in Exchange Online sharing with another organization running Exchange on-premises, kindly monitor future Message Center posts for guidance on migration paths as they become available. 

Additional information:

• Migration guide: Migrating to Microsoft 365 Cross-Tenant Access Policy for sharing Free/Busy, Calendars, and MailTips.
• Exchange Online EWS, Your Time is Almost Up
• Deprecation of EWS in Exchange Online 
• Enhancing Microsoft 365 security by eliminating high-privilege access