TL;DR: The most common fix is re‑registering the AAD Broker Plugin via PowerShell. Jump straight to Solution 3 to get back into Outlook quickly.
If you’re staring at the error “A required authentication broker is missing” while trying to sign in to the Outlook desktop app, you’re not alone. This issue has been frustrating Microsoft 365 users across Windows 10 and 11, often blocking access to Teams, Excel, and other Office apps as well. The good news? It’s usually fixable without reinstalling Windows.
What Causes This Error?
The “authentication broker” is a core Windows component—the Web Account Manager (WAM) —that safely handles sign‑ins for Microsoft 365 apps. When it becomes corrupted, disabled, or blocked, desktop apps can’t verify your credentials even though the web versions (outlook.office.com) continue to work.
Common triggers include:
- A recent Windows Update or Office update.
- A password change or Multi‑Factor Authentication (MFA) reset.
- Third‑party antivirus or security software interfering.
- A corrupted user profile linked to device registration.
How to Fix the “Authentication Broker Missing” Error
These solutions are ordered from least invasive to most advanced. Try them in sequence.
1. Restart the Web Account Manager Service
Sometimes the service simply needs a restart.
- Press Windows Key + R, type
services.msc, and press Enter. - Scroll down to Web Account Manager.
- Right‑click it and select Restart.
- Try signing into Outlook again.
2. Clear Windows Credentials
Old cached credentials can block the new authentication flow.
- Close all Microsoft 365 apps (Outlook, Teams, etc.).
- Open Control Panel → User Accounts → Credential Manager.
- Click Windows Credentials.
- Under Generic Credentials, look for entries containing
MicrosoftOfficeorADAL. - Click the arrow next to each one and select Remove.
- Restart your computer and try to sign in again.
3. Re‑register the Authentication Broker via PowerShell
This is the most reliable fix recommended by Microsoft engineers. It re‑installs the broker plugin.
- Close all Microsoft 365 apps.
- Open PowerShell (right‑click and choose Run as Administrator—this ensures the command applies system‑wide).
- Copy and paste the following command (make sure the quotes are straight
"and not curly):
Add-AppxPackage -Register "$env:windir\SystemApps\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy\Appxmanifest.xml" -DisableDevelopmentMode -ForceApplicationShutdown- Press Enter and wait for the operation to complete.
- Restart your device, then open Outlook and test the sign‑in.
4. Rename the AAD Broker Plugin Folder
If re‑registering doesn’t work, renaming the broker’s data folder forces Windows to recreate a fresh copy.
- Close all Microsoft 365 apps.
- Press Windows Key + R, type
%localappdata%\Packages, and press Enter. - Find the folder named
Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy. - Rename it (right‑click → Rename) by adding
.oldto the end, e.g.,Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy.old. - Restart your computer. Windows will automatically create a new, healthy copy of the folder.
5. Check Security Software & Work/School Account
- Third‑party antivirus: Temporarily disable (or uninstall) your antivirus to see if it’s blocking the broker. If the error disappears, add an exclusion for the broker folder (
%localappdata%\Packages\Microsoft.AAD.BrokerPlugin_*) or switch to a less intrusive security suite. - Work/School account: Go to Settings → Accounts → Access work or school. If your account is listed, try Disconnect then Connect again. This refreshes your device registration with Azure AD.
6. Use the Web Apps as a Temporary Workaround
If you need immediate access while troubleshooting, remember that the web versions of Outlook, Teams, and Office work perfectly. Go to outlook.office.com to check your email.
When to Contact Your IT Admin
If your device is managed by an organization (company or school), you may encounter this error due to Intune policies or device enrollment restrictions. If none of the steps above resolve the issue, contact your System Administrator. They may need to check device registration or provide a fix specific to your environment.
Helpful Resources & Links
For further reading, these official Microsoft Q&A threads provide additional context and solutions:
- [Microsoft Q&A] Getting error while accessing outlook, teams and excel
https://learn.microsoft.com/en-au/answers/questions/5819705/getting-error-while-accessing-outlook-teams-and-ex - [Microsoft Q&A] A required authentication broker is missing, how do I fix it?
https://learn.microsoft.com/en-us/answers/questions/5233468/a-required-authentication-broker-is-missing-how-do - [Microsoft Q&A] Windows 11 Authentication and Taskbar Issues
https://learn.microsoft.com/en-nz/answers/questions/2283173/windows-11-authentication-and-taskbar-issues - [Microsoft Q&A] How do I edit Web Account Manager? (365 Outlook password problem)
https://learn.microsoft.com/en-us/answers/questions/4516963/how-do-i-edit-web-account-manager-(365-outlook-pas
Looking for more ways to boost your Microsoft 365 productivity? Check out our guide: [Top 10 Microsoft 365 Productivity Tips for 2026] – link to another Mukunda Software post.
