Running Office 2024 LTSC - Outlook has begun prompting for Office login

For me, the solution was to set and apply the following registry-settings. I have no idea why this made the issue go away, or how autodiscover is part of the problem . . . We where already running the setting for "Exclude initial check to Office 365 Autodiscover URL"

Hi Carl,

My name is Jason and I am an independent advisor and windows user like yourself.

You're not alone—this issue has been cropping up for several organizations running Office 2024 LTSC with on-prem Exchange, especially after recent updates. Here's a breakdown of what's likely happening and how to mitigate it: Root Cause

Office 2024 LTSC appears to be increasingly integrated with Microsoft 365 cloud services, even when running in a strictly on-premises environment. Despite registry keys like SignInOptions = 3 and ExcludeExplicitO365Endpoint = 1, Outlook may still attempt to reach out to Azure AD endpoints due to:

• Modern Authentication fallback attempts
• Background service discovery (e.g., Autodiscover redirecting to Office 365)
• Office licensing telemetry or activation checks
• Recent Office updates re-enabling cloud hooks

This behavior is especially common when:

• Users have no Microsoft 365 account associated
• Smartcard login is used for AD authentication
• Modern Auth is not deployed on Exchange on-prem

Recommended Fixes

1. Disable Modern Authentication in Outlook

Even if you're not using Modern Auth, Outlook may still attempt it. Add this registry key:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity] "EnableADAL"=dword:00000000

This disables Azure AD Authentication Library (ADAL) and forces Outlook to use legacy auth.

2. Block Autodiscover to Office 365

Ensure Outlook doesn't redirect to cloud endpoints:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover] "ExcludeExplicitO365Endpoint"=dword:00000001 "ExcludeHttpsRootDomain"=dword:00000001 "ExcludeHttpsAutoDiscoverDomain"=dword:00000001 "ExcludeSrvRecord"=dword:00000001

This blocks Autodiscover from reaching Office 365 and cloud services.

3. Disable Office Sign-In Globally

You already have SignInOptions = 3, but double-check this key:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Internet] "UseOnlineContent"=dword:00000000

This disables online content and cloud integration features.

4. Check GPOs and Licensing

• Ensure Group Policy isn’t re-enabling cloud features.
• Confirm Office LTSC is properly activated and not falling back to Microsoft 365 licensing checks.

5. Update Outlook to Latest LTSC Patch

Some builds of Office 2024 LTSC introduced aggressive cloud hooks. Updating to the latest patch may reduce this behavior Microsoft Learn justinho.com.

Optional Diagnostic

If you're comfortable with deeper inspection:

• Use Fiddler or Procmon to trace Outlook's network calls.
• Check for any calls to login.microsoftonline.com, autodiscover.outlook.com, or office365.com.

Hi again!

Adding the recommended registry keys did not unfortunately fix the issue. I have seen this additional issues:

Trying to login to Office no longer gives the option to login with a certificate or a smart card. We only get the password prompt, which we cannot use as we are passwordsless.

Trying to create a new Outlook-profile also begins to prompt for a password, after several tries it suddenly created a new profile . . .

When trying to login to Office, Office tells me that "It seems this e-mail address are used by more then one Microsoft account. Which do you want to use?"

We can choose between "Work or school account" - with the email address "@havochvatten.se" or we can choose "Personal account" - with the email address "@havochvatten.se"

Regarding the registry key to disable the Office Sign-in (SignInOptions = 3), there is another problem that have occured.

We have some users that we sync to our AzureAD to allow them to sign in to external SharePoint sites for collaboration.

When these users are not signed in to Office, they can no longer switch from editing Office documents in SharePoint to their local desktop version of Office. I think this issue started after we upgraded from Office 2021 LTSC to 2024 LTSC. For these users we allow sign in to Office.

Regarding the problem of random Office login prompts, they occur both for users that are synced to our AzureAD and users that are not. But for the users that are not synced to our AzureAD´(and have the "SignInOptions = 3" set), they don´t see the login prompt, but instead an error stating "The administrator have disabled this feature", which makes sense . . .

Thank you very much for your answer! This is somewhat correlating to my own suspicions. I will try this on some affected users immediately!