Mostly after assigning permissions for a Room Mailbox in Office 365 the permissions are not correctly synchronized to Outlook clients. I created cases at Microsoft for this “bug” but it seems a fix for this annoying issue is still far away. However instead of waiting for days (or eternity) there is something you can do to fix this within minutes!
What’s happening at the client
When a user wants to add the room mailbox to Outlook and then creating an appointment he/she will be presented with this error:
How to fix it
Everything you click in Office 365 is in fact a Powershell cmdlet running in the background. Instead of trusting the GUI for this we can assign the permissions directly via Powershell. Luckily it’s proven already that this is working without issues.
First connect Powershell to Office 365. For the ones who don’t know how to do this, here is the script:
$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirectionImport-PSSession $Session
Now, even after assigning full access in the GUI you can check if your permissions are really set correctly with this cmdlet Get-MailboxFolderPermission -Identity email@example.com:\Calendar
After assigning myself full access permission in the GUI I am not able to retrieve this information via Powershell as you can see above.
Now assign the permissions directly by performing this cmdlet Add-MailboxFolderPermission -Identity firstname.lastname@example.org:\Calendar -User email@example.com -AccessRights Owner
You will still have some synchronization time for users but just give Outlook a restart after a couple of minutes and you will see he/she is now able to add the Room Mailbox and create appointments in it.