I've created a MailUser (no mailbox) account for an application service. When I try to delegate access to the required users' calendars I get the following:
[PS] C:\WINDOWS\system32>Add-MailboxFolderPermission -AccessRights Author -User zzzz -Identity yyyy:\Calendar The user "zzzz" was found in Active Directory but isn't valid to use for permissions. Try an SMTP address instead.+ CategoryInfo : NotSpecified: (:) [Add-MailboxFolderPermission], InvalidInternalUserIdException+ FullyQualifiedErrorId : [Server=xxxx,RequestId=ae8aa027-e2d6-4c80-9b34-4e6668bb47c2,TimeStamp=6/12/2014 6:43:28 PM] [FailureCategory=Cmdlet-InvalidInternalUserIdException] D5F9F342,Microsoft.Exchange.Management.StoreTasks.AddMailboxFolderPermission+ PSComputerName : xxxx [PS] C:\WINDOWS\system32>Add-MailboxFolderPermission -AccessRights Author -User zzzz@xxxx.xxx -Identity yyyy:\Calendar The user "zzzz@xxxx.xxx" is either not valid SMTP address, or there is no matching information.+ CategoryInfo : NotSpecified: (:) [Add-MailboxFolderPermission], InvalidExternalUserIdException+ FullyQualifiedErrorId : [Server=xxxx,RequestId=c0a02976-4ce3-45cf-9599-f8032c7cc1d5,TimeStamp=6/12/2014 6:43:35 PM] [FailureCategory=Cmdlet-InvalidExternalUserIdException] 5DB0C177,Microsoft.Exchange.Management.StoreTasks.AddMailboxFolderPermission+ PSComputerName : xxxx
Justin Cervero - MS Enterprise Admin - Appalachian State University