The error message is Failed to commit transaction: Failed to add backlink from CN=Default,CN=OWA Mailbox Policies,CN=Samba,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=exchange,DC=home,DC=matws,DC=net to CN=Default,CN=OWA Mailbox Policies,CN=Samba,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=exchange,DC=home,DC=matws,DC=net - attribute 'msExchOWATranscodingMimeTypesBL': value #0 on 'CN=Default,CN=OWA Mailbox Policies,CN=Samba,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=exchange,DC=home,DC=matws,DC=net' already exists It looks like we don't check when we create the backlink if the attribute already exists. I think we also have issues when removing linked attributes pointing to ourselves