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Resolve persistent authentication prompts in Outlook

David Nguyen 185 Reputation points
2026-04-06T04:59:43.09+00:00

Hi there,

The context is after migrating to Modern Authentication (OAuth) in a Microsoft 365 environment, some of my users experience repeated credential prompts and intermittent disconnections, even though login succeeds and MFA is completed.

Outlook | Windows | Classic Outlook for Windows | For business
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  1. Hani-Ng 11,155 Reputation points Microsoft External Staff Moderator
    2026-04-06T05:53:05.6366667+00:00

    Hi David Nguyen

    According to my research, here is a checklist for your review:

    Clear Cached Credentials & Reset WAM:

    • Credential Manager: Open Windows Credential Manager and delete any entries starting with MicrosoftOffice16, Outlook, or ADAL.
    • Windows Settings (WAM): Go to Settings > Accounts > Access work or school. Find the M365 account, click Disconnect, and then Connect to re-add it. (Note: Do not disconnect the account if it is the primary Entra ID/Azure AD device join).

    Force Modern Auth via Registry: Ensure Outlook isn't falling back to Basic Auth by verifying/adding these DWORD values:

    • HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity
      • EnableADAL = 1
    • HKEY_CURRENT_USER\Software\Microsoft\Exchange
      • AlwaysUseMSOAuthForAutoDiscover = 1

    Verify Tenant & Client Readiness

    • Check Exchange Online PowerShell to ensure Modern Auth is enabled globally: 
        Get-OrganizationConfig | FL OAuth2ClientProfileEnabled
      (Must be True).
    • Ensure users are on supported Outlook versions.

    Check Network & Conditional Access

    • Network: VPNs, proxies, or SSL inspection can sever OAuth tokens. Temporarily bypass the VPN to test.
    • Entra ID: Check Azure AD Sign-in Logs for the affected users. Look for "Interrupted" statuses, which often point to Conditional Access policies evaluating repeatedly.

    Create a New Outlook Profile

    If the issue is isolated to a few users, their Autodiscover cache may be corrupted. Recreating the profile via Control Panel > Mail > Show Profiles will force a clean OAuth connection.

    Once configured correctly, users should only see one prompt per token lifetime. Outlook should remain connected silently in the background without loops.

    I hope this helps and if you have any update, please let me know via comment section! Thank you.

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

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  2. AI answer

    2026-04-06T05:00:03.09+00:00

    Use the following targeted checks and fixes to stabilize Outlook after moving to Modern Authentication.

    1. Force Outlook to use Modern Authentication for Autodiscover/EWS If any affected users still connect to an on-premises mailbox via RPC (or have an old RPC-based profile) plus Exchange Online, Outlook may fall back to legacy auth and repeatedly prompt.

    On each affected Windows device:

    1. Close Outlook.
    2. Open regedit.exe.
    3. Go to: 
         HKEY_CURRENT_USER\Software\Microsoft\Exchange
    4. Create a new DWORD (32-bit) Value named: 
         AlwaysUseMSOAuthForAutoDiscover
    5. Set Value data to 1.
    6. Close Registry Editor and restart Outlook.

    This forces Outlook to use Modern Authentication for Autodiscover and related web services instead of RPC-compatible schemes.

    1. Fix profiles that continually prompt for credentials If users see a constant password prompt and “trying to connect…” when connecting to Microsoft 365, the profile may be using an incompatible logon security setting.

    For older Outlook builds that still expose this setting:

    1. Close Outlook.
    2. Open Control Panel → Mail → Email Accounts → select the Exchange/Microsoft 365 account → Change → More Settings.
    3. On the Security tab, set Logon network security to Anonymous Authentication.
    4. Restart Outlook and test.

    For newer Outlook 2013/2016 builds, this setting is disabled/removed and the issue is typically resolved by those updates. Ensure Office is fully updated and then:

    • Run the Microsoft 365 diagnostic Diag: Outlook keeps asking for my password as referenced in the documentation to automatically check for common causes.
    1. Clear cached credentials and identity data Repeated prompts after a successful Modern Auth sign-in can also be caused by bad cached credentials or identity cache corruption.

    On Windows clients:

    1. Close all Office apps.
    2. Open Control Panel → Credential Manager → Windows Credentials.
    3. Remove entries related to Outlook, Microsoft Office, or Microsoft 365.
    4. In C:\Users\<UserName>\AppData\Local\Microsoft, remove the folders identitycache and oneauth (as per the documented support guidance).
    5. Restart Outlook and sign in again with Modern Authentication and MFA.
    6. For mixed or migrated environments (hybrid / RPC history) If users were migrated from on-premises Exchange that used RPC, or still have additional on-premises mailboxes in their profile, combine the above with:
    • Ensuring the profile is recreated against Exchange Online so that all connections are using Modern Authentication.
    • Applying the AlwaysUseMSOAuthForAutoDiscover registry key to avoid Outlook choosing RPC-style auth paths that do not support Modern Authentication.
    1. Mac clients (if any users are on Outlook for Mac) For Outlook 2016 for Mac users who see repeated Modern Auth prompts:
    2. Ensure Outlook 2016 for Mac is updated to at least version 15.31.0.
    3. If prompts persist, clear duplicate tokens from Keychain:
      • Quit all Office apps.
      • Open Keychain Access.
      • Search for Exchange and delete items for the affected account.
      • Search for adal and delete items of type MicrosoftOffice15_2_Data:ADAL:<GUID>.
      • Search for office and delete Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2.
      • Restart Outlook and re-authenticate.

    These steps address the main documented causes of persistent prompts and intermittent disconnects after enabling Modern Authentication: Outlook falling back to RPC-compatible auth, incompatible logon security settings, and corrupted cached credentials/tokens.

    References:

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