Exchange Online users can't add on-premises conference rooms to meeting requests in Outlook Web App
Original KB number: 2904381
Symptoms
In a hybrid deployment of on-premises Microsoft Exchange Server and Exchange Online, assume that Exchange Online users select add room in a meeting request in Outlook Web App. In this situation, on-premises room mailboxes aren't displayed in the list as expected. Therefore, Exchange Online users can't add an on-premises conference room to a meeting request.
Cause
This issue occurs if the recipientTypeDetails property of on-premises room mailboxes is set to MailUser.
When a room mailbox is created in the cloud, its recipientTypeDetails property is set to RoomMailbox. In a hybrid environment, on-premises room mailboxes are synced to the cloud through directory synchronization. After directory synchronization occurs, the recipientTypeDetails property of on-premises room mailboxes is set to MailUser.
Resolution
Add on-premises mailboxes to an on-premises room list. To do this, open the Exchange Management Shell on the on-premises Exchange server, and then run the following cmdlets:
New-DistributionGroup -Name <NameOfRoomList> -roomlist
Add-DistributionGroupMember <NameOfRoomList> -member <OnPremisesRoomMailbox>
Note
A room list has a limit of 100 room mailboxes per room.
More information
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