Outlook login fails authentication_package_v1 for 3 users at random times. Windows 11 Pro 22H2 Delete Exchange/Outlook profile Recreate, ensure disable anonymous login Install all Windows and Outlook updates Deleting Outlook 2021 Installing Office 2021 Version 2401 Delete Windows Credentials for all SSPI and Office entries Check Outlook connection status, review failure lid 40480 error code 10 Event 4776 C0000064 user name does not exist Disable modern authentication; edit the Windows Registry on your computer, then go here: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover\ExcludeExplicitO365Endpoint /d 0

Hi @Gerald Ho , Welcome to our forum！ It seems like you've been having some trouble with Outlook 2016/2021 constantly asking for your password and you have tried many troubleshooting steps. Could you clarify when this issue first started and if any changes were made before it began? Also, does the password prompt only appear when you're logging in or does it enter the "password required" state without any interaction? If it's the latter, we recommend trying the method outlined in this document . Besides, you could reset the passwords of affected users. Additionally, it's worth checking if any firewalls or security software may be blocking the authentication process. Hope the above information is helpful to you！ If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 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.

Outlook 2016/2021 keeps asking for password, fail authentication_package_v1 leading to lockout on premise Exchange

Gerald Ho 0

Outlook login fails authentication_package_v1 for 3 users at random times.

Windows 11 Pro 22H2
Delete Exchange/Outlook profile
Recreate, ensure disable anonymous login
Install all Windows and Outlook updates
Deleting Outlook 2021
Installing Office 2021 Version 2401
Delete Windows Credentials for all SSPI and Office entries
Check Outlook connection status, review failure lid 40480 error code 10

Event 4776 C0000064 user name does not exist Disable modern authentication; edit the Windows Registry on your computer, then go here: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover\ExcludeExplicitO365Endpoint /d 0

2 answers

Wandi Ding -MSFT 2,870 Reputation points Microsoft Vendor

2024-02-02T05:55:58.03+00:00

Hi @Gerald Ho ,

Welcome to our forum！

It seems like you've been having some trouble with Outlook 2016/2021 constantly asking for your password and you have tried many troubleshooting steps.

Could you clarify when this issue first started and if any changes were made before it began? Also, does the password prompt only appear when you're logging in or does it enter the "password required" state without any interaction? If it's the latter, we recommend trying the method outlined in this document. Besides, you could reset the passwords of affected users. Additionally, it's worth checking if any firewalls or security software may be blocking the authentication process.

Hope the above information is helpful to you！

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 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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Gerald Ho 0 Reputation points

2024-02-02T22:19:12.23+00:00

Hello Wandi Ding, The suggested resolution is for Outlook 365, and two of the three problems are with Outlook 2016. On one station the user reported the issue while using Outlook. They noticed the yellow exclamation mark (normally Online Exchange) and offline Exchange, then the login box appeared. The credentials where entered three times and then the problems began. The other two users cannot confirm exactly when the problem started, but the symptoms are the same. They can enter their password three times until they are locked out. Today, I've deleted all the Windows Credentials and 1799f21e7c124640b14a8c0bc873a3db - Autodiscover.xml and old certificates; added the correct certificate to Trusted Root Certification. Reset user password Event 4776 continues at a much higher rate for these three users, than another users. Which would indicate authentication problems, but looking at the Outlook Connection Status, the error ratio is only recording the number of times after the account lockout.

Wandi Ding -MSFT 2,870 Reputation points Microsoft Vendor

2024-02-06T07:17:00.42+00:00

Thanks for the details and first of all apologies for my previous misunderstanding. Event 4776 is logged when the computer attempts to verify the credentials of an account. A high occurrence of these events for a specific user may indicate repeated failed login attempts. Have you tried disabling any third-party add-ins in Outlook? Also, although it's a bit strange, you might try Set-OrganizationConfig -OAuth2ClientProfileEnabled $true to see if that resolves the issue.

Gerald Ho 0 Reputation points

2024-02-07T14:32:36.4466667+00:00

There aren't any Outlook add-ins. The only third-party is Adobe Acrobat. The Event 4776 is a credential problem, but when an Outlook 2016/2021 profile is created, the password is entered and then cached. What mechanism is sending an incorrect password, and leaving the user 1 possible login attempt (most times they have already been locked out when prompted for credentials)? Most of the time, and for other users it's working as expected, however lately these specific users are being locked out. I've deleted the Windows credentials and SSO_POP_DEVICE and SSI keep getting created Don't want to change the OAuth for the other existing clients that are working fine. May create additional problems.

Wandi Ding -MSFT 2,870 Reputation points Microsoft Vendor

2024-02-21T09:15:44.91+00:00

Sorry for the late reply, is there any update on this issue?

Gerald Ho 0 Reputation points

2024-02-21T21:04:45.85+00:00

Then problem persists. Found this security event precedes the fail;

A user's local group membership was enumerated.

This event is generated when a process attempts to log on an account by explicitly specifying that account’s credentials. This most commonly occurs in batch-type configurations such as scheduled tasks, or when using the RUNAS command

Wandi Ding -MSFT 2,870 Reputation points Microsoft Vendor

2024-02-23T06:40:08.78+00:00

We are still researching the issue and if there are any updates, I will provide feedback here as soon as possible.

Gerald Ho 0 Reputation points

2024-04-26T18:37:47.8233333+00:00

Problem continues after April 2nd update. After user closes Outlook or leaves Outlook open on the desktop and doesn't touch the system for 10 minutes, user is locked out without prompting for password.

autodiscover.xml and windows stored credentials deleted, and the user still gets locked out.

Tested registry fix; ExcludeExplicitO365Endpoint, ExcludeSrvRecord, ExcludeScpLookup

Schannel A fatal error occurred while creating a TLS client credential and Security SSP scheduled Software Protection service for re-start errors on the workstation. Exchange Add-in for desktop was removed and readded when the system was logged out
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