Cross-Tenant Shared Meeting Room Spaces

Set up a two-way organization relationship with free/busy sharing. Booking then works because the resource mailbox auto-accepts. Check ProcessExternalMeetingMessages on the rooms though, it's off by default and that's usually why cross-tenant booking silently fails.

The GAL is the real gap. Org relationships share free/busy, not directory objects, so rooms in tenant B won't appear in tenant A's GAL or room finder. Cross-tenant sync in Entra doesn't help, it's built for user objects. Most people create mail contacts in each tenant pointing at the other tenant's rooms. Crude, but it gets them selectable. Room finder still won't work since it needs local room lists.

Nothing extra on the Teams side. If there are Teams Rooms devices, the account stays in one tenant and joins the other's meetings as an external participant.

Worth asking whether a tenant merge is on the cards. Maintaining contacts for shared resources across two tenants gets old fast.