Whilst working on an Office 365-Exchange 2007 hybrid environment, you may experience errors similar to those shown below from the Directory Synchronization Error Report email and in Forefront Identity Manager: Identity Error Description DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}@exchangelabs.co.uk Unable to update this object in Microsoft Online Services, because the attribute Username is not valid. Update the value in…