A widespread problem is when Outlook?keeps asking for the user credentials, even if the correct password is specified. After starting Outlook successfully connects to the on-premises Exchange server (or Microsoft 366/Office 365 mailbox), the user sees a list of folders in the mailbox and new emails in the Inbox folder. But after a few minutes, a window appears for entering the user name and password. The user enters the password and presses OK, but the window with the prompt to enter the credentials appears again and again. By clicking the “Cancel” button, the user can continue to work with Outlook, and after a while, the password request window pops up again (sometimes the user account may be locked).? The problem occurs in different versions of Outlook (2019/2016/365) and Windows (there was a problem in both Windows 7/8.1 and Windows 10/11).

When such a problem occurs, HelpDesk team members usually try to re-create the mail profile and/or repair/re-install Office.? But this usually does not help. Outlook still requires the user to enter a password at some interval.

Let’s take a look at a few tips to help you get rid of the annoying password prompt in Outlook.

Clearing Cached Credentials for Outlook on Windows

Check if you have Outlook saved credentials (passwords) stored in Windows Credential Manager, try to remove them all. To do this, go to Control Panel\All Control Panel Items\User Accounts\Manage your credential -> Windows Credentials. Find the saved passwords for Outlook/Office in the Generic Credentials list and remove them.

To directly access Credential Manager, run the command:

rundll32.exe keymgr.dll,KRShowKeyMgr

Disable the “Always Prompt for Credentials” Option in Outlook

Open your Outlook Account Settings (File -> Account Settings -> Account Settings), double click on your Exchange account. Go to More settings -> select Security tab. Clear the checkbox Always prompt for credentials in the User identification section. In this case, Outlook will first try to use the cached credentials to access the mailbox.

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Security
Type: Reg_Dword 
Name: PromptForCredentials 
Value:0

Prevent internet connection in the Office Trust Center settings:

1. In Outlook, select File -> Options –> Trust Center-> Trust Center Settings;
2. Go to the Privacy Options;
3. Uncheck the option Let Office connect to online services from Microsoft to provide functionality that’s relevant to your usage and preferences. In Outlook 2013, this option is called Allow Office to connect to the Internet;
   https://docs.microsoft.com/en-us/outlook/troubleshoot/authentication/password-prompt-at-every-start-or-cannot-create-profile
   
4. If you are using GPO administrative templates for MS Office, this setting can be configured with the policy parameter Online Content Options = Do not allow Office to Connect to the Internet under the following GPO section: Administrative Templates -> Microsoft Office 2016 -> Tools | Options | General | Service Options -> Online Content.

If you have a Microsoft 365 (Office 365) mailbox connected in Outlook, this tab should have an additional field Logon network security. Make sure Anonymous Authentication is not selected here.

Disable Office 365 Autodiscover in Outlook

Somewhere in the fall of 2016, an update was released for Outlook 2016 that enabled a mandatory check of the connection endpoint in the Microsoft 365 (Office 365) cloud. You can verify this by using the Fiddler or TCPView tools to monitor the attempts to connect to the autodiscover-s.outlook.com and outlook.office365.com servers.

If you are using a non-Office365 mailbox or an on-premises Exchange mailbox, Outlook will try to detect detecting your Microsoft account even though the Autodiscover is not pointed to Microsoft 365.

You can disable this check for an on-premise Exchange Server. Go to the registry key HKEY_CURRENT_USER\Software \Microsoft\Office\16.0\Outlook\AutoDiscover and create a new DWORD parameter named ExcludeExplicitO365Endpoint and value 1. Restart Outlook.

You can make changes to the registry with the following command:

reg add HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\AutoDiscover /t REG_DWORD /v ExcludeExplicitO365Endpoint /d 1
Or, using the PowerShell cmdlet Set-ItemProperty:
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Outlook\AutoDiscover" -Name 'ExcludeExplicitO365Endpoint' -Value 1 -Type DWORD –Force

The ExcludeExplicitO365Endpoint registry parameter is applicable to Outlook 2016 and 2019 (this key is in addition to the list of keys that determine how Autodiscover is performed when Outlook starts).

Outlook Prompts for Password After Migrating to Microsoft 365 (EOL)

If your mailbox has been migrated from on-premises Exchange to Microsoft 365 or you have two mailboxes connected in Outlook (one from the on-premises Exchange, the second from Microsoft 365/Exchange Online) and you use an RPC connection. In this case, Outlook doesn’t use Modern Authentication (also used for MFA). In this case, your credentials are sent to Office 356 instead of a token. To force Outlook to use Modern Authentication for RPC connections, you need to add the AlwaysUseMSOAuthForAutoDiscover DWORD parameter with the value 1 to the registry key HKCU\Software\Microsoft\Exchange.

Set-ItemProperty -Path " HKCU:\Software\Microsoft\Exchange" -Name 'AlwaysUseMSOAuthForAutoDiscover' -Value 1 -Type DWORD -Force

Make sure Modern Authentication is enabled for your account in the Microsoft 365 Admin Center (Settings -> Services & add-ins).