$users = Get-MailBox | Where {$_.ResourceType -eq "Room"} | Select -ExpandProperty Alias
Foreach ($user in $users) {Set-MailboxFolderPermission $user":\Calendar" -user Default -accessrights Reviewer}
of als je het per room wilt instellen met het subject erbij kies je voor deze:
Get-MailboxFolderPermission roomname@domain.com:\Calendar Set-MailboxFolderPermission -Identity "roomname@domain.com:\Calendar" -User default -AccessRights PublishingAuthor Set-CalendarProcessing -Identity "roomname@domain.com" -AddOrganizerToSubject $true -DeleteComments $false -DeleteSubject $false