Outlook repeatedly asks for my Microsoft 365 work account password after every restart

The supported causes and safest repair path are:

1. Client-side authentication state is the first thing to verify Since the work account works in Outlook on the web and on mobile, the mailbox and password are valid. The documented Windows-side cause for Microsoft 365 app authentication failures is broken local authentication components, including the Microsoft Entra WAM plugin for work accounts.
2. Run Microsoft’s sign-in diagnostics first Use the Microsoft 365 Sign-in troubleshooter. It is specifically recommended for common Microsoft 365 sign-in issues and is the safest first diagnostic step.
3. Repair the Windows authentication component for the work account For a work account, the documented repair is to reinstall the Microsoft Entra WAM plugin package from an elevated PowerShell window:

      if (-not (Get-AppxPackage Microsoft.AAD.BrokerPlugin)) { Add-AppxPackage -Register "$env:windir\SystemApps\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy\Appxmanifest.xml" -DisableDevelopmentMode -ForceApplicationShutdown } Get-AppxPackage Microsoft.AAD.BrokerPlugin
   

   This targets the work-account sign-in component and does not remove the mailbox.
4. If the issue is with the personal account sign-in component instead, repair the Live ID package separately For personal accounts, the documented package is different:

      if (-not (Get-AppxPackage Microsoft.Windows.CloudExperienceHost)) { Add-AppxPackage -Register "$env:windir\SystemApps\Microsoft.Windows.CloudExperienceHost_cw5n1h2txyewy\Appxmanifest.xml" -DisableDevelopmentMode -ForceApplicationShutdown } Get-AppxPackage Microsoft.Windows.CloudExperienceHost
   

   Because the repeated prompt is for the work or school account, the WAM plugin repair is the directly relevant step.
5. For classic Outlook only, check the Exchange account security setting if the build is affected A documented cause of repeated Microsoft 365 password prompts in affected older Outlook versions is Logon network security being set to something other than Anonymous Authentication. Path:
   • Close Outlook
   • Open Control Panel → Mail
   • Show Profiles → select the profile → Properties
   • E-mail Accounts → select the Exchange account → Change
   • More Settings → Security tab
   • Set Logon network security to Anonymous Authentication
   Microsoft notes that Outlook 2016 and some recent Outlook 2013 builds are not affected because that setting was disabled or removed in newer builds. This step applies only if that setting exists in the classic Outlook profile.
6. If classic Outlook profile corruption is involved, recreate the profile cleanly The supported profile reset path is:
   • Close Outlook
   • Open Control Panel → Mail
   • Show Profiles
   • Remove old profiles
   • Create a new profile
   • Add the work account first
   • Test Outlook
   • Then add the personal Outlook.com account
   This aligns with the documented and accepted troubleshooting pattern for repeated prompts and mixed personal/work account instability.
7. What the available documentation supports about root cause The available support content supports these possibilities:
   • Broken Windows authentication components for Microsoft 365 apps, specifically the Microsoft Entra WAM plugin for work accounts.
   • Cached credentials or profile corruption in Outlook.
   • In affected classic Outlook versions, an incorrect Logon network security setting.
   The available content does not provide a supported basis to conclude that the cause is a damaged Windows user profile or a Microsoft Entra sign-in policy. It only notes that if device registration still fails after local cleanup, an organization’s IT administrator may need to check Entra ID devices, sign-in logs, or Conditional Access.
8. Safest repair order for this scenario To avoid affecting the personal Microsoft 365 subscription or deleting the organizational mailbox, use this order:
   1. Run the Microsoft 365 Sign-in troubleshooter.
   2. Repair the Microsoft Entra WAM plugin package.
   3. In classic Outlook, check Logon network security only if that setting exists.
   4. Create a new Outlook profile and test the work account first.
   5. If the problem still persists and there are signs of registration or policy issues, have the organization’s administrator review Entra ID devices, sign-in logs, and Conditional Access.
9. Risk note Avoid registry-based Outlook profile edits unless specifically required. Microsoft states that modifying the Outlook profile through the registry is not supported and can leave the profile in an unsupported state.

References:

• Fix authentication issues in Microsoft 365 apps when you try to connect to a Microsoft 365 service
• Outlook continually prompts for your password when you try to connect to Microsoft 365
• Adding one exchange account from work and one personal account doesn't work in Outlook classic - Microsoft Q&A
• Outlook work account keeps prompting for password or fails to connect - Microsoft Q&A