How to "redirect" Outlook logins back to on-premise Exchange

Recent Office updates have been "accidentally" redirecting Outlook users who use on-premise Exchange environments to login to Office 365. These have been known to cause, at best annoyances with the extra useless login prompts, and at worst full disconnections from on-premise Exchange.

The workarounds below attempt to gain back control for your Outlook. But we all know that these workarounds are temporary. Office updates will continue with their "cat-and-mouse" games.

Tell Outlook to skip the Microsoft 365 endpoint during the Autodiscover process

reg add "HKCU\Software\Microsoft\Office\16.0\Outlook\AutoDiscover" /v "ExcludeExplicitO365Endpoint" /t REG_DWORD /d 1

Delete Outlook caches the "O365-only" identity

reg delete "HKCU\Software\Microsoft\Office\16.0\Common\Identity\Identities"

Tells Outlook to use the classic Windows Auth instead of the modern Microsoft login (which is using ADAL or Azure AD Authentication Library).

reg add "HKCU\Software\Microsoft\Office\16.0\Common\Identity" /v "EnableADAL" /t REG_DWORD /d 0
reg add "HKCU\Software\Microsoft\Office\16.0\Common\Identity" /v "DisableADALatopWAMOverride" /t REG_DWORD /d 1

Recent Office updates have introduced "Autodiscover V2" and "Direct Online Connect" behaviors that sometimes ignore the classic registry keys above. Disable these.

reg add "HKCU\Software\Microsoft\Office\16.0\Outlook\AutoDiscover" /v "DisableAutodiscoverV2Service" /t REG_DWORD /d 1
reg add "HKCU\Software\Microsoft\Office\16.0\Common\Internet" /v "UseOnlineContent" /t REG_DWORD /d 0

Clear the "Identity" Cache in AppData

rmdir /s "%localappdata%\Microsoft\IdentityCache"
rmdir /s "%localappdata%\Microsoft\OneAuth"
rmdir /s "%localappdata%\Microsoft\Outlook\RoamCache"