Introduction
Seeing an Outlook sign-in error can be frustrating. The April 27, 2026 outage has produced widespread “Account Not Authenticated” messages, but sign‑in problems can also occur on normal days for many reasons.
This guide covers the most common causes and their fixes. If you first want to confirm whether a global outage is underway, use our guide to checking Outlook status .
“Account Not Authenticated”
This error typically means Microsoft’s authentication servers cannot verify your credentials. During a global outage, wait for Microsoft’s fix. On a normal day, a corrupted browser cache or an outdated app can cause it. Clear your browser cache and cookies, or try signing in from a different browser. On mobile, update the Outlook app to the latest version. If the problem persists, remove and re‑add your account. For more workarounds, see our alternatives guide .
Unexpectedly Signed Out
Many mobile users affected by the April 27 outage found themselves suddenly signed out. Do not uninstall the app. Wait until Microsoft confirms service restoration, then try signing in again. If the issue occurs outside an outage, check that your device’s date and time are set automatically. An incorrect system clock can break secure connections.
Two‑Factor Authentication Problems
If you use two‑factor authentication (2FA), ensure the app or device generating your code is synced. If you recently changed phones or lost access to your authenticator app, use a backup recovery code. Microsoft’s account recovery process can help. For a step‑by‑step recovery walkthrough.
Persistent Password Errors
Double‑check that caps lock is off. If you recently changed your password, the old one may be cached. Clear your browser’s saved passwords and try again. For account recovery steps after a hack, refer to the Outlook account recovery guide .
Conclusion
If you see “Account Not Authenticated” during a known outage, your best action is to wait. For persistent problems on normal days, the steps above resolve most sign‑in errors. For a complete timeline of Microsoft’s reliability issues, see our Microsoft 365 outage history .