Problem:
When signing into Outlook Web (Outlook.com or Microsoft 365 webmail), some users are met with a 401 Unauthorized error. This error occurs when the login request cannot be validated, meaning Microsoft’s servers don’t recognize the provided credentials or block access for security reasons.
Common scenarios include:
- You enter the correct username and password, but the page shows 401 – Unauthorized.
- After entering login details, the page reloads or shows an error without opening your mailbox.
- Two-Factor Authentication (2FA) codes are not accepted, leading to repeated login failures.
- Outlook works fine on mobile or desktop apps but fails in the web browser.
This issue can disrupt personal communication (missing important messages or password reset emails) and business operations (employees locked out of Microsoft 365 accounts, missing deadlines, and meeting invites).
Solution:
While a 401 error usually means the server is rejecting your login request, it can be caused by multiple factors—from browser cache issues to Microsoft account security settings. Here’s a step-by-step guide to fix it:
1. Confirm Microsoft Service Status
First, rule out a global outage:
- Visit status.office.com for real-time service health updates.
- Check @MSFT365Status on Twitter/X for outage announcements.
- If Microsoft lists an incident, the error may resolve once they restore service.
2. Clear Browser Cache and Cookies
Old session data often triggers authentication failures.
- Open Chrome/Edge → Settings → Privacy & Security → Clear browsing data.
- Select Cookies and Cached files → Clear data.
- Restart the browser and attempt login again.
3. Use Private Mode or Another Browser
- Open Incognito (Ctrl+Shift+N) in Chrome or Private Window in Edge/Firefox.
- Try logging in again. If this works, the issue is likely caused by cached cookies or an extension.
4. Disable Browser Extensions
Ad blockers, VPNs, or password managers can sometimes interfere with Microsoft’s login process.
- Go to chrome://extensions/ and disable them one by one.
- Test Outlook after disabling each extension to identify the culprit.
5. Check Account Credentials & 2FA
- Make sure your Microsoft account password is correct by signing in at account.microsoft.com .
- If you use Two-Factor Authentication, ensure your device time is correct and try backup codes or SMS verification.
- If you’ve recently changed your password, update it in all connected devices (phone apps, desktop Outlook) to avoid conflicts.
6. Reset Your Password if Necessary
If you still get the 401 error even with the right password, reset it:
- Go to Microsoft Password Reset .
- Follow the prompts to set a new, strong password.
- Re-add your account in Outlook if needed.
7. Network and Security Checks
- If you’re using a VPN or proxy, disable it and try logging in again.
- Check that your firewall or antivirus is not blocking Microsoft login URLs.
- If you’re on a corporate network, ask your IT team if restrictions are in place.
8. Use Alternative Access Until Fixed
If you still can’t log in on Outlook Web, use other access methods temporarily:
- Outlook desktop app or mobile app (iOS/Android).
- IMAP/SMTP settings in clients like Thunderbird or Apple Mail.
- Microsoft Teams for urgent communications if available in your Microsoft 365 plan.
Final Thoughts
The Outlook Web 401 Unauthorized error can be frustrating, but it’s often caused by cached browser data, conflicting login sessions, or Microsoft’s authentication issues. By clearing cookies, checking service status, updating credentials, and trying alternative access methods, most users can regain access quickly.
For business users, keep staff informed, provide temporary communication alternatives, and monitor Microsoft’s Service Health updates. If the issue persists after trying all solutions, contact Microsoft Support for assistance.
