Calendar Problems

How to Share Meeting Room Availability Across Microsoft 365 Tenants

Khadija Khan Oct 7, 2026 869 views

Question details

The user needs to configure calendar free/busy sharing so that organizations in different Microsoft 365 tenants can view meeting room availability and book shared rooms.

How to Share Meeting Room Availability Across Microsoft 365 Tenants

Product: Microsoft 365
Device & OS: not provided
Scenario: Two or more organizations share a physical office space but operate on entirely separate Microsoft 365 tenants, requiring them to cross-reference shared meeting room availability.
Observed behavior: By default, users in one Microsoft 365 tenant cannot see the free/busy calendar information or book meeting rooms located in a separate tenant.

Before you start

Ensure you have Microsoft 365 global administrator or Exchange administrator privileges in both tenants, as creating an organization relationship requires administrative access.

Solution 1Recommended

Configure an Exchange Online Organization Relationship

Set up an organization relationship between the two Microsoft 365 tenants to allow seamless calendar free/busy sharing and meeting room bookings.

An Exchange Online organization relationship allows organizations to securely share calendar availability information with external Microsoft 365 tenants. By configuring this relationship mutually across both tenants, users can view when shared meeting rooms are booked and request reservations.

Access the Exchange Admin Center

Sign in to the Microsoft 365 admin center using your administrator credentials and navigate to the Exchange Admin Center (EAC).

Navigate to Organization Sharing

In the left navigation pane of the EAC, click on 'Organization' and then select 'Sharing'.

Create a New Organization Relationship

Under the 'Organization sharing' section, click the 'Add' (+) button to create a new relationship configuration.

Specify External Tenant Domains

Enter the primary domain names of the external Microsoft 365 tenant with which you are sharing the meeting rooms.

Enable Free/Busy Sharing

Toggle the settings to turn on calendar free/busy information sharing. You can choose to share only time, or time, subject, and location depending on your privacy requirements.

Configure an Exchange Online Organization Relationship

Enable External Processing for Room Mailboxes: For external users to successfully book the shared rooms, you must also ensure the room mailboxes are configured to process external meeting requests by using the Set-CalendarProcessing PowerShell cmdlet with the -ProcessExternalMeetingMessages $true parameter.

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Frequently Asked Questions

Why can't external users book the meeting room after setting up the organization relationship?

Setting up the organization relationship only allows free/busy calendar viewing. To allow external users to book the room, the room's mailbox must be specifically configured to accept external meeting requests using the 'ProcessExternalMeetingMessages' setting in Exchange.

How long does it take for calendar sharing to work across tenants?

Once the organization relationship is configured in both Microsoft 365 tenants, it can take up to 24 hours for the new calendar sharing policies and free/busy permissions to fully propagate.

Will calendar sharing expose sensitive details of other meetings?

No, administrators have full control over the level of detail shared. The relationship can be configured to only show 'Free/Busy' times without revealing meeting subjects, attendees, or internal locations.

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