Can’t Log Into Microsoft Teams or Outlook?

For many businesses running on Microsoft 365, Teams and Outlook are the daily engines of collaboration. When those logins stop working—especially on a busy Monday morning—it can bring productivity to a screeching halt.

Maybe you’re an IT manager for a healthcare group that depends on Teams to coordinate patient scheduling, or you run a multi-location real estate firm where Outlook is the heartbeat of every client conversation. Either way, “Can’t sign in” isn’t just an inconvenience—it’s downtime that costs time, trust, and revenue.

Fortunately, not every login issue means a major outage. In many cases, the fix is simple. Here’s how to diagnose common Microsoft Teams and Outlook sign-in problems, confirm whether it’s something you can handle yourself, and know when it’s time to call support.

Check the Basics—Because They Still Matter

Ever hear of that logistics firm with 20 drivers who reported Outlook connection errors every Monday. It turned out their shared Wi-Fi extender at HQ dropped overnight, forcing devices offline. A quick restart of the extender fixed the “server timeout” issue instantly.

Consider this a reminder that, before diving into deeper technical troubleshooting, verify the simple stuff first.

1. Confirm your internet connection.
   If other cloud services are slow or timing out, your connection—not Microsoft—may be the culprit. Try another network, or run a quick test (like Fusion Connect’s Speed Test Plus) to check for packet loss or latency.
2. Restart the app and device.
   It sounds obvious, but cached sessions or hung background processes can block authentication. Rebooting clears them out.
3. Verify credentials.
   If you’re using saved passwords, they may have expired since your last successful login.

Clear Cache and Stored Credentials

Teams and Outlook cache old session data and credentials to speed up logins—but that cache can occasionally get corrupted, leading to failed authentication.

For Microsoft Teams:

• Quit Teams completely
• Navigate to %appdata%\Microsoft\Teams (on Windows) or ~/Library/Application Support/Microsoft/Teams (on macOS)
• Delete everything inside the Cache, blob_storage, databases, and Local Storage folders
• Relaunch Teams and sign in again

For Outlook:

• On Windows, open Control Panel > Mail > Profiles, and remove/recreate the user profile
• Clear any stored passwords under Credential Manager
• Restart Outlook and re-add the account

If the issue clears, the cache was likely to blame. If not, keep going.

Watch for Account Lockouts and MFA Loops

A dental group using Microsoft 365 through Fusion Connect saw recurring Teams lockouts across several offices. The culprit? An employee’s old phone still had the Authenticator app installed, sending invalid MFA requests. Once IT removed the outdated device from AAD, the issue vanished.

This happens often…in many small-to-medium organizations, multi-factor authentication (MFA) is managed centrally through Azure Active Directory (AAD). That means expired tokens or repeated password failures can trigger lockouts—especially when users try to reauthenticate from multiple devices at once.

Here’s what to check:

• Has your password recently changed? If so, ensure it’s updated on every device—mobile, desktop, and web
• If you’re getting repeated MFA prompts, open a private/incognito browser and try signing in fresh
• Confirm your MFA device (like the Microsoft Authenticator app) is still registered and synced to your current phone

If repeated lockouts persist, your organization’s admin may need to reset your sign-in state or reissue credentials.

Check Browser and App Compatibility

We recently heard about a marketing agency who reported that Teams web access failed for half their staff—but only in Chrome. Updating Chrome to the latest version and clearing cookies resolved the problem instantly. Maybe that could work for you?

If you’re logging into Teams or Outlook via browser and seeing blank screens or endless redirects, compatibility could be the cause.

Try this to text your browser:

1. Make sure your browser is current (Teams works best in the latest versions of Microsoft Edge, Chrome, and Safari)
2. Disable extensions—especially ad blockers, privacy tools, or password managers that can intercept authentication redirects
3. Clear cookies and cached site data
4. Test in a private/incognito window

For the desktop versions, verify your client version is up to date. Outdated clients sometimes can’t negotiate modern authentication protocols required by Microsoft 365.

Check Microsoft’s Service Health Dashboard

Sometimes, it really isn’t you. Microsoft periodically experiences regional authentication outages that can impact Teams, Outlook, and the Microsoft 365 sign-in portal. Before burning hours troubleshooting, check the Microsoft 365 Service Health Dashboard (admins) or Microsoft Support updates.

If the issue is listed there, your best move is to monitor updates and wait—it’s a global issue, not a local one.

When to Call Support

If you’ve cleared cache, confirmed credentials, checked MFA, and ruled out browser and Microsoft-side issues, it’s time to escalate.

Here’s when you should contact your IT administrator or Fusion Connect’s 100% U.S.-based Support team:

• Repeated MFA or password lockouts across multiple users
• No sign-in access despite verified credentials
• Persistent “We couldn’t sign you in” errors on all devices
• Authentication loops that continue after cache and browser resets

Because Fusion Connect provides Microsoft 365 licensing, Teams Calling Services, and Managed Network connectivity, our support engineers can look beyond the surface—helping identify whether the issue is within Microsoft 365, your authentication infrastructure, or your network edge.

Final Thoughts: Simplify Support Before the Next Lockout

Login errors can feel random, but the root causes usually fall into a few predictable buckets—cache corruption, outdated credentials, MFA sync issues, or browser misbehavior. With a quick checklist and an understanding of what’s local versus global, you can get your users back online fast.

And if you’re ready to spend less time chasing logins and more time driving collaboration, Fusion Connect’s Microsoft-certified experts can help streamline your environment—from licensing and Teams Calling to secure managed connectivity.

Visit Fusion Connect's Microsoft Licensing to learn how we help businesses like yours stay connected, secure, and productive.

Fusion Connect is a next-generation Managed Communications Service Provider (MCSP) and Microsoft Cloud Solution Provider.

*Microsoft, Microsoft 365, and Microsoft Teams are trademarks of the Microsoft group of companies.