Outlook personal email not working

Question

Client Id: [moderator note: PII removed]

Session Id: [moderator note: PII removed]

Client Version: 20260313003.08

BootResult: fail

Back Filled Errors: Unhandled Rejection: SyntaxError: Failed to execute 'json' on 'Response': Unexpected end of JSON input:undefined|undefined:undefined|undefined:undefined|undefined:undefined

err: Error: 401

esrc: StartupData

et: ServerError

estack: Error: 401

st: 401

[moderator note: PII removed]

Answer 1

Hi D. Brown,

I understand it’s concerning when a personal Outlook email suddenly stops working and shows technical messages during sign-in.

I can see there is already a Q&A Assist answer in the thread, and its guidance is generally aligned with common sign-in and authentication scenarios for Outlook.com. Before adding more context, did you have a chance to try the steps suggested there, and if so, what was the result?

First, a quick note on scope: this is a public, user-to-user forum, so fellow users can guide troubleshooting, but we don’t have access to account or server-side logs. To avoid making assumptions and to ensure the next steps are relevant, I’d like to clarify a few points about your situation first:

1. Does this happen only on Outlook on the web (browser), or do you see the same behavior in the Outlook app on mobile/Windows/Mac as well?
2. Which browser and device are you using (Edge/Chrome/Firefox/Safari + Windows/Mac/iOS/Android)? And does it behave the same way in a private window?
3. Can you sign in successfully at your Microsoft account page (account services), and the problem occurs only when opening the mailbox at Outlook.com - or are you blocked earlier during sign-in?
4. Does another Outlook.com/Hotmail account open normally on the same device/browser, or is it happening to all accounts?

In the meantime, here are quick checks you can try:

1. Open a private/incognito browser window and sign in to Outlook.com from there (this helps confirm whether saved cookies/session data is involved).
2. If private mode works, clear cookies/site data for Microsoft/Outlook sites, fully close the browser, then sign in again.
3. Check the Microsoft page for recent Outlook.com issues/workarounds (this helps confirm whether there’s an active service-side incident affecting access). https://support.microsoft.com/en-us/office/fixes-or-workarounds-for-recent-issues-on-outlook-com-8c95d913-d96b-4065-9171-e1fa44b03ff5

Once these are clarified, I can add some additional information specific to your scenario.

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Since this is a public forum, we will hide your personal identifiable information, and I have sent that image of yours containing your personal identifiable information in a private message so we can work together to resolve the issue. Also, please check your private message in case you want to share another screenshot to avoid leaking your PII by click on the Private Message button as show below.

Answer 2

The error details show HTTP status 401 during Outlook.com web startup, which indicates an authentication/authorization failure when loading startup data.

Based on the provided context, the most relevant guidance is for Outlook.com connectivity and authentication issues:

1. Verify sign-in method
   • Sign out of Outlook.com completely.
   • Close all browser windows and clear cookies/cache for Outlook.com/Microsoft sites.
   • Open a new browser session and sign back in at Outlook.com, ensuring the correct account and password are used.
2. Check for Basic vs modern authentication
   • Some apps and scenarios using Basic authentication to connect to Outlook.com can fail or show repeated prompts as security is tightened.
   • Always use the built‑in Outlook.com option in any mail app’s “Add account” flow when available.
   • If using another email application or integration, confirm with that application’s support that it supports OAuth against EAS, POP, IMAP, and SMTP. If it does not, expect increased login prompts and potential failures as Basic Auth is phased out.
3. Try Outlook apps as an alternative
   • If Outlook.com web continues to fail in the browser, use the free Outlook apps, which are designed to work with modern authentication:
     • Outlook for Windows from the Microsoft Store
     • Outlook for Mac from the Mac App Store
     • Outlook for iOS from the iOS App Store
     • Outlook for Android from the Google Play Store
4. If the issue persists
   • Use the Outlook Forum on Answers or Outlook Tech Community to provide the error details (including the 401 status and the StartupData reference) so support agents and engineers can review server‑side issues specific to the account or region.

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References:

• Outlook and other apps are unable to connect to Outlook.com when using Basic authentication