I can swear I’ve blogged about this already, but I cannot seem to find it, so here we go again.
Configuring resource delegates via PowerShell is no longer possible for User mailboxes in Exchange Online. The –ResourceDelegates parameter of the Set-CalendarProcessing cmdlet designates recipients to which calendar requests will be forwarded, in scenarios where you have chosen to delegate calendar access. In Outlook, you can do this by accessing the Delegate Access dialog, adding a user and select the “Delegate receives copies of meeting-related messages sent to me” checkbox.
Previously, it was possible to control these settings via PowerShell as well, but if you try to use the Set-CalendarProcessing cmdlet now to add/remove resource delegates, you will run into the following error:
Set-CalendarProcessing vasil -ResourceDelegates pesho ResourceDelegates can only be enabled on resource mailboxes. + CategoryInfo : InvalidData: (vasil:ADObjectId) [Set-CalendarProcessing], ResourceOnlyException + FullyQualifiedErrorId : [Server=AM5PR03MB3027,RequestId=68f34b77-37b3-4783-830e-e78186874768,TimeStamp=5/18/2017 3:30:02 PM] [FailureCategory=Cmdlet-ResourceOnlyException] 5491BFF2,Microsoft.Exchange.Management.StoreTasks.SetCalendarProcessing + PSComputerName : outlook.office365.com
If you need to control these settings, you will have to use Outlook or EWS-based script.
As to when this change occurred, I’m pretty sure it was around the time I blogged about a similar change with the –AddNewRequestsTentatively parameter.