Hi, Yesterday there was the following scenario with a customer. - User mailboxes were migrated with third party tools to a new Office 365 tenant. - UserPrincipalName stayed the same. - Employees used the same laptop and profiles than before. - Exchange Hybrid was built to manage users. - AutodiscoverInternalUri was nulled. When customer started creating new Outlook profiles, there was an error with autodiscover usage. It seemed that it cannot find dns-records, but everything was in-place and created correctly. ADAL prompt flashed really quickly onscreen and then disappeared. The reason for this behavior was ADAL and the old identities inside Registry. Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities and remove all identities. Or just disable ADAL completely. Windows Registry Editor Version 5.00 "EnableADAL"=dword:00000000 After this You will get Old Sk00l login prompt for Outlook and everything works.
