Cross-tenant Free/Busy, MailTips, and Calendar Sharing are moving to Cross-Tenant Access Policy

This blog post discusses a feature that is not yet fully available. Please see The rollout schedule for Cross-Tenant Access Policy table below for expected availability dates.

If your organization shares Free/Busy, MailTips, or calendars with other Microsoft 365 organizations, there's a change coming that you'll want to understand and plan for. If it doesn't, you can stop reading in about two paragraphs. This post covers what's changing as Exchange Web Services (EWS) is deprecated, how the new Microsoft 365 Cross-Tenant Access Policy model replaces the old plumbing, how to tell whether your tenant is affected, and what to do about it. The official announcement is Message Center post MC1446796; consider this the friendlier, more complete version with the context we wish the MC post had room for.

Is your organization impacted by this change?

Only if your organization shares Free/Busy, Calendars, or MailTips information with other Microsoft 365 organizations.

This change affects cross-tenant / cross-organization collaboration - the ability for people in your organization (Organization A) and people in a partner's Microsoft 365 tenant (Organization B) to see each other's Free/Busy availability, shared calendars, and MailTips (such as out-of-office notices). If you've set up these relationships with subsidiaries, partners, vendors, or recently acquired companies, you need to understand this and take action before the deadline, or those experiences will break.

Organization sharing is not set up by default – tenant admins must have set it up by themselves.

Not impacted scenarios:

• Sharing Free/Busy availability, calendars, or MailTips within your organization.
• Sharing Free/Busy availability, calendars, or MailTips between your on-premises and online users in an Exchange Hybrid Deployment. You should work on your Dedicated Hybrid App as per our previous announcements.
• Sharing Free/Busy availability, calendars, or MailTips with another organization running on-premises Exchange. Watch for future Message Center posts covering this scenario (no immediate impact but changes are coming). If you are sharing with a partner organization running both Exchange Online and on-premises, the sharing with Exchange Online is impacted.

The “How to check your sharing configurations?” section below has more information on how to verify.

What's changing, and why

Deprecation of Exchange Web Services (EWS) begins on October 1, 2026. Several cross-tenant collaboration features - Free/Busy, MailTips, and Calendar Sharing – currently use  Exchange Web Services under the hood. As EWS is retired in Exchange Online, the mechanism that carries those cross-tenant requests has to move somewhere else.

That “somewhere else” is Microsoft 365 Cross-Tenant Access Policy. It replaces the EWS-based approach, and it becomes available starting September 2026. The end state is the same experience your users have today - someone sees a colleague's calendar availability across a tenant boundary - but it travels over a modern, Entra-governed path instead of legacy EWS. It's part of the broader push to retire legacy protocols and eliminate high-privilege access.

How the new model works

Today, three Exchange Online configurations drive cross-tenant sharing:

• Organization Relationships - used to share Free/Busy and MailTips with other Microsoft 365 tenants.
• Availability Address Spaces - used to share Free/Busy with other Microsoft 365 tenants (specifically those set with AccessMethod: OrgWideFBToken).
• Sharing Policies - used to share calendars externally, either through invitations sent to recipients in other Microsoft 365 organizations, or calendars published for anonymous access via an internet URL.

Historically, each of these has used EWS to fetch availability and MailTips from the partner tenant. Going forward, that trust and data exchange is expressed through Microsoft 365 Cross-Tenant Access Policy instead. You still decide which partner organizations you collaborate with and what you share; only the mechanism carrying it changes. Migrating means understanding your current configuration, standing up the equivalent Cross-Tenant Access Policy, validating that sharing still works, and then removing the old configurations you no longer need.

How to check your sharing configurations?

MC1446796 was sent to every tenant but most admins who received it won't actually need to do anything. So before you plan a migration, confirm you're in scope. Run these three commands in Exchange Online PowerShell:

Get-OrganizationRelationship | Format-List Name, DomainNames, Enabled, FreeBusyAccessEnabled, FreeBusyAccessLevel, FreeBusyAccessScope, MailTipsAccessEnabled, MailTipsAccessLevel, MailTipsAccessScope

You're affected if the results show Enabled: True, and either FreeBusyAccessEnabled: True or MailTipsAccessEnabled: True, and the external organization is hosted in Microsoft 365. Otherwise, no action is needed.

Get-SharingPolicy | Format-List Name, Domains, Enabled, Default

You're affected if the results show Enabled: True, the Domains property contains at least one rule with a CalendarSharingFreeBusy access level (Simple, Detail, or Reviewer), the targeted external organization is hosted in Microsoft 365, and the policy is assigned to one or more mailboxes. Otherwise, no action is needed.

One note on that last check: rules that begin with Anonymous: represent calendar publishing to anonymous internet recipients through a published URL, and they show up in the same output. If you have an Anonymous: rules with a CalendarSharingFreeBusy access level (Simple, Detail, or Reviewer) then you are affected.

Sharing Free/Busy with another organization hosted in Microsoft 365 via Availability Address Space (with AccessMethod OrgWideFBToken) does not depend on Exchange Web Services and is not impacted by EWS deprecation. However, you may still wish to migrate these configurations to Microsoft 365 Cross-Tenant Access Policy, which supports additional security features and more granular configuration options. Run this command to check your Availability Address Space configurations:

Get-AvailabilityAddressSpace | Format-List ForestName, AccessMethod

The rollout schedule for Cross-Tenant Access Policy

This feature becomes available starting September 2026, so your migration window opens as the rollout reaches your environment. Here's the schedule:

What happens if you do nothing?

Starting October 1, 2026, EWS will be gradually disabled in Exchange Online, in line with the deprecation communications we've been sending for a while now. As that rollout reaches your tenant, any cross-tenant Free/Busy, MailTips, and Calendar Sharing that still depends on EWS will stop working - people in your partner organizations may no longer see Free/Busy, MailTips, or shared calendars coming from your tenant. You may no longer be able to see Free/Busy, MailTips, or shared calendars from the partner organization. If you're in scope and take no action, that's the outcome.

Not ready by October? You have a runway

We realize that the window between this announcement and the start of the rollout is short. For organizations with many partner tenants and a tangled web of organization relationships, analyzing, testing, and executing a migration in a few weeks is a tall order, and we know it.

There is a safety valve. You can keep the existing cross-tenant sharing working by setting EWSEnabled to True, following the guidance in our earlier post, Exchange Online EWS, Your Time Is Almost Up. That keeps the old path alive while you prepare and execute the migration. This extension remains available until the final EWS shutdown on April 1, 2027 - which is the hard deadline for completing the move.

You do not need to specify AppIDs in your tenant Allow List to keep the old method working, as it doesn’t rely on AppIDs (as it doesn’t use OAuth). If EWSEnabled is set to True, we’ll allow the cross-tenant flows covered here to continue working until April 2027, no matter the tenant Allow List state.

What you need to do

1. Confirm scope. Run the checks above. If nothing flags, you're done.
2. Plan your migration for after the rollout reaches your tenant and before EWS deprecation affects you. Review the migration guide for step-by-step instructions.
3. Migrate - understand your current configurations, set up the new Microsoft 365 Cross-Tenant Access Policies, validate that sharing works, and remove the configurations you no longer need.
4. If you can't finish by October 1, set EWSEnabled to True to keep sharing alive until you can migrate, no later than April 1, 2027.

Further reading

• Message Center post MC1446796 - Migrate Free/Busy, MailTips, and Calendar Sharing before EWS deprecation (the official announcement in your tenant).
• Migrating to Microsoft 365 Cross-Tenant Access Policy for sharing Free/Busy, Calendars, and MailTips (the migration guide).
• Exchange Online EWS, Your Time Is Almost Up (how to keep EWS running with EWSEnabled while you migrate).
• Deprecation of EWS in Exchange Online.

Frequently Asked Questions

 

We cannot make the October deadline for this migration. Other than setting EWSEnabled to True for our tenant, do we need to add some AppID to the tenant EWS Allow List?
Setting EWSEnabled to True is all that you need to do to keep your current configurations for sharing with other organizations working. You do not need to add anything to the EWSAllowedAppIDs tenant value. Please note that both your and your partner Microsoft 365 organization need to set EWSEnabled to True to continue bidirectional information sharing.

What happens if we set up sharing using the new model on my side but the partner organization does not?
For bidirectional sharing, both organizations need to configure Microsoft 365 Cross-Tenant Access Policies and disable the old configurations before sharing will work in both directions.
For one-way sharing, only the resource tenant (the tenant with the mailboxes that contain the Free/Busy, Calendar, or MailTips information) needs to configure a Microsoft 365 Cross-Tenant Access Policy. Once configured, users in the home tenant (the tenant with users trying to access the shared information) will be able to access the information via Cross-Tenant Access Policy. Ensure both organizations disable old configurations for sharing as these will prevent requests from flowing through the new Cross-Tenant Access Policy.

What happens if we extend EWS deprecation in my tenant but the partner organization does not and we do not complete the migration before EWS deprecation starts?
After EWS is disabled in the partner organization, users in your organization will no longer be able to access information shared from the partner organization. Users in the partner organization will continue to be able to access information shared from your organization.

We have a Sharing Policy with a Wildcard in the domain. Do we need to migrate it?
Yes, as long as the CalendarSharingFreeBusy access level is Simple, Detail, or Reviewer.

Our default Sharing Policy is defined (with a "{*:0}" wildcard domain) but is set to Enabled:False. This is because we want to prevent users from external calendar sharing. Do we need to migrate this policy?
No action is needed. No Cross-Tenant Access Policy will have an equivalent effect to default Sharing Policy being disabled.

What if we are sharing with multiple domains that are in the same partner Tenant ID?
Create a single Microsoft 365 Cross-Tenant Access Policy to configure sharing with the partner Tenant ID. Any domains associated with the partner Tenant ID will be covered by the policy.

What if we have an Availability Address Space with Google Workspace for Google/Exchange Calendar Interop?
You are not affected by this change. Users in Exchange Online can continue to access calendar information of users in Google Workspace via the Availability Address Space configuration. Users in Google Workspace can continue to access calendar information of users in Exchange Online via Microsoft Graph API. Ensure Google Workspace is configured to connect to Exchange Online via Microsoft Graph API and not the legacy EWS connection method. See: Allow Google Calendar users to see Exchange availability

What if we have an Availability Address Space configuration for sharing Free/Busy between commercial cloud (most customers world-wide) and 21Vianet cloud?
Availability Address Space (with AccessMethod OrgWideFBToken) does not depend on Exchange Web Services and is not impacted by EWS deprecation. However, you may still wish to migrate these configurations to Microsoft 365 Cross-Tenant Access Policy, which supports additional security features and more granular configuration options.

Major updates to this blog post:

• 9/11/2026: Added a banner to the blog post
• 9/3/2026: Removed a redundant section of the article.
• 8/28/2026: Various updates to the post; timeline changes, several clarifications made.
• 8/18/2026: Modified the FAQ related to AAS sharing with the 21Vianet cloud.
• 8/10/2026: Added a FAQ that clarifies that default sharing policy that is set to be disabled does not need migration.

The Exchange Online EWS Deprecation Team