OPTION 1 - Disconnect the Work or School account in Windows Settings. To do this, use the following method. First close down Outlook. Hold the Windows + I keys simultaneously to open the Settings window. Then click Accounts > Access work or school to open the accounts settings options.
Now highlight the account you're having issues with and click Disconnect. Once done, open Outlook and you should now be prompted for your username and password.
OPTION 2 - Add these registry keys
- [HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover]
- “PerferLocalXML”=dword:00000001
- “ExcludeHttpRedirect”=dword:00000000
- “ExcludeHttpsAutoDiscoverDomain”=dword:00000001
- “ExcludeHttpsRootDomain”=dword:00000001
- “ExcludeScpLookup”=dword:00000001
- “ExcludeSrvRecord”=dword:00000001
- “ExcludeLastKnownGoodURL”=dword:00000001
- “ExcludeExplicitO365Endpoint”=dword:00000001
OPTION 3 - Disable Modern Authentication by regedit to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, create a DWORD item named EnableADAL and set it to zero.
OPTION 4 - Under the same registry key, create a DWORD item named DisableADALatopWAMOverride and set it to 1.
OPTION 5 -Add the following 3 keys under HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity:
Create a DWORD 32 bit value named DisableADALatopWAMOverride and set it to 0
Create a DWORD 32 bit value named DisableAADWAM and set it to 0
Create a DWORD 32 bit value named EnableADAL and set it to 1
I know some of these steps are opposite from each other, but each one has fixed it in the past, depending on the situation.
NOTE: If you try Option 2, 3, 4, or 5 and it doesn't fix it, be sure to delete the key you created. Just to keep things clean and not cause problems later on.