User can't accept a meeting invitation for a room mailbox in Outlook if the delegate is a shared mailbox

Applies to: Exchange OnlineOutlook 2016Outlook 2013


Consider the following scenario.
  • You add a shared mailbox as a delegate for a room mailbox by running the following PowerShell command:
    Set-CalendarProcessing room -ResourceDelegates sharedmbx -AllBookInPolicy $false -AllRequestInPolicy $true 
  • When a user tries to accept the meeting invitation from the Inbox of the shared mailbox in Microsoft Outlook, they receive an error message that resembles the following: 
    Cannot open the Calendar folder for user "room alias". The operation failed.

  • The user can accept the meeting request from the Inbox of the shared mailbox in Outlook on the web. However, the user who sent the meeting request doesn't receive an email message that confirms that the meeting was accepted. 


This behavior is by design. Users who have access to the shared mailbox don't inherit permissions to the calendar of the room mailbox. 


Users who have full access permission to the shared mailbox must have explicit editing permissions to the calendar of the room mailbox. To assign editing permission to users for the calendar of the room mailbox, follow these steps:
  1. Do one of the following, as appropriate for your situation:
  2. Run the following command:
    Add-MailboxFolderPermission -Identity\Calendar -User -AccessRights Editor 
    Note In this command, replace with the email address of the room, and replace with the email address of the user who has full access permissions to the shared mailbox.


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