Forum Discussion
Cross-Tenant Shared Meeting Room Spaces
We have two M365 tenancies under our group. We need to allow users from both tenants to use Meeting room resources (book rooms, use calendars etc..). Is this just about configuring Exchange OR Sharing in EXO or do we need anything beyond that to facilitate Teams meeting room resource sharing?
Would we also need to sync these meeting room objects across tenancies to allow users to see them in GAL etc.. ?
Thank you!
4 Replies
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.
Cross Tenant calendar sharing would be one that you can try. An organization relationship or mailbox level sharing so users can see room availability. Also, creating mail contacts for other tenant room to make them available in outlook GAL.
To allow users from two M365 tenants to share meeting room resources like booking rooms and accessing calendars, the key step is setting up proper calendar and mailbox sharing in Exchange Online. You’ll need to configure cross-tenant calendar sharing and delegate permissions so users can book rooms across both environments. Beyond that, for Teams meeting room resource sharing, no extra Teams-specific setup is usually needed if Exchange sharing is in place. However, syncing meeting room objects in the Global Address List (GAL) across tenants isn’t automatic—you’d need to set up directory synchronization or use a third-party solution if you want the rooms visible in both tenants’ GAL. Hope that helps!
It's really up to you. Enable the room mailboxes to process external meetings, and go from there. If you want the room's visibility to be exposed cross-tenants, you need to configure an org relationship (sharing policies are mostly targeted at end user scenarios): https://learn.microsoft.com/en-us/exchange/sharing/organization-relationships/create-an-organization-relationship
For the purpose of processing external meetings and fetching free/busy it is not necessary to have the room objects synced across tenants, but if you want to expose them in the GAL, you can provision contacts. Keep in mind that the end user experience for those will be different from adding room mailboxes in the "home" tenant, and you cannot add them to room lists either.
