Unexpected sub status (6008)

Dear @PETE DRANEY,

The error“The credential is invalid. Unexpected sub status (6008)” in Outlook typically indicates a local authentication or cached‑credential problem on the device, not a problem with the mailbox itself. It is most often seen when adding a Microsoft 365 work or school account to the Outlook desktop app on Windows.

In this case, please try these steps below and check if it works:

Step 1: Confirm the account itself is valid

Before changing anything locally, verify this points to a device issue:

1. Open a browser and sign in at https://office.com or https://outlook.office.com
2. Sign in using the same account you are adding to Outlook

• If sign‑in works > The credentials are valid, continue with the steps below
• If sign‑in fails > Reset the password or check account status with your admin

Step 2: Clear cached Microsoft credentials

1. Close Outlook and all Microsoft apps (Teams, Word, Excel, OneDrive)
2. Open Credential Manager
   • Control Panel > Credential Manager
   • Select Windows Credentials
3. Remove all Microsoft/Office-related entries, especially:
   • MicrosoftOffice
   • Office16
   • Outlook
   • ADAL
   • MSOID
   • mso
4. Restart the computer

Step 3: Reset Azure AD (Entra ID) cached tokens

1. Press Win + R, paste: %localappdata%\Packages\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy
2. Delete all contents of that folder (do not delete the folder itself)
3. Restart Windows

Step 4: Reconnect the work or school account in Windows

1. Go to Settings > Accounts > Access work or school
2. Select your work account > Disconnect
3. Restart the PC
4. Return to the same screen and Connect the account again
5. Add the account back to Outlook

Note: If none of the above solutions work, let me know for further investigation. Please note that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.   

Kindly let me know the outcome after trying the steps above. Thank you very much for your valuable time and your cooperation.

I am looking forward to your response!

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".   

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The error indicates a problem validating the credentials when adding the account. Use these steps to resolve it:

1. Remove any cached or conflicting credentials
   • Open Control Panel → Credential Manager → Windows Credentials.
   • Remove entries related to Outlook, Microsoft 365, or the email address being added.
   • Close Credential Manager.
2. Ensure the account is unique and not duplicated at another provider
   • If the same email address and password are also used at a third‑party provider (for example, a hosted mailbox with the same address), this can cause Outlook setup failures.
   • Either:
     • Create and use a different alias in Microsoft 365 (for example, ******@contoso.onmicrosoft.com) to set up Outlook, then authenticate with the main Microsoft 365 address when prompted, or
     • Change the username or password on the third‑party account so it is not identical to the Microsoft 365 account.
3. Try adding the account again
   • Start Outlook and add the account using the updated alias or after clearing credentials.

If the issue persists, verify with the domain or hosting provider that Autodiscover and authentication for the domain are correctly configured and not returning unexpected responses.

References:

• Connection to Microsoft Exchange is unavailable error when a Microsoft 365 user tries to set up Outlook
• Gmail IMAP won't connect to Classic Outlook - Microsoft Q&A Can't add new Gmail IMAP account to Classic Outlook. Error msg: We weren't able to set up your Google account with IMAP. You may need to make changes to your Gmail settings.
• Do you know how to fix the issue where Outlook keeps prompting for a password even though credentials are saved - Microsoft Q&A