I get this error message when I try to launch Microsoft outlook cloud. How can I fix this?

Question

UTC Date: 2026-03-20T02:53:45.438Z
Client Id: EBF34473319343679D947778E3126039
Session Id: f358cd21-cf81-4c98-b735-917ab6aa2b91
Client Version: 20260313003.07
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
    at Object.y [as createStatusErrorMessage] (https://res.public.onecdn.static.microsoft/owamail/hashed-v1/scripts/owa.mailindex.d7a889c9.js:2:299125)
    at https://res.public.onecdn.static.microsoft/owamail/hashed-v1/scripts/owa.mailindex.d7a889c9.js:2:23649
st: 401
efe: BN9PR03CA0843

Answer 1

Hello, I'm Quinn and here to help!

The error you're seeing is a 401 Unauthorized issue, which means Outlook on the web is having trouble verifying your sign-in session during startup. Before escalating, it's worth trying a few quick fixes, but if those don't work, this type of error can be service-side and may require Microsoft Support to resolve on the backend.

Before trying these methods, try accessing it using a different browser to quickly check if the issue is browser-specific.

Method 1: Clear Browser Cache & Cookies

1. Press Ctrl + Shift + Delete
2. Select Cookies and other site data and Cached images/files
3. Set the time range to All time
4. Click Clear data
5. Restart your browser and try again

Method 2: Sign Out and Sign Back In

1. Go to http://outlook.office.com/
2. Click your profile icon
3. Select Sign out
4. Close all browser tabs
5. Reopen the browser and sign in again

Method 3: Use Private / Incognito Mode

1. Press Ctrl + Shift + N (Chrome/Edge)
2. Open Outlook in the private window
3. Sign in with your account

Method 4: Try Another Browser or Device

1. Open Outlook in a different browser (Edge, Chrome, or Firefox)
2. Alternatively, use another device (phone or another PC)
3. Check if the issue still occurs

Method 5: Sign Out of All Microsoft Accounts

1. Before signing out, make sure you have your passwords, 2FA codes, and recovery codes ready so you don't get locked out
2. Go to https://account.live.com/proofs/Manage/additional
3. Sign out of all accounts
4. Close the browser completely
5. Reopen it and sign in with only the affected account

Answer 2

The error details show a 401 (unauthorized) response while Outlook on the web is starting up. In the provided context, similar “Something went wrong”/startup failures for Microsoft 365 web experiences have ultimately required service-side fixes by Microsoft support.

Because the issue is tied to authentication/authorization on the service, and local troubleshooting (browsers, cache, devices, networks) is often not sufficient, the supported path is:

1. If part of a Microsoft 365 tenant, ask the Microsoft 365 admin to open a support case from the Microsoft 365 Admin portal and include the error details (401 status, Client Id, Session Id, UTC Date).
2. If using a consumer Microsoft account, open a support ticket through the Microsoft 365/Outlook consumer support channel and provide the same diagnostic information.

For Outlook access while the issue is being investigated, use an alternative client that still works for the account (for example, Outlook classic for Windows or another working entry point such as Outlook mobile).

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References:

• Outlook IMAP or POP server unexpectedly terminated the connection, and the server was interrupted
• Error when opening classic Outlook: "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed."
• New Outlook has stopped working, Fails when starting after 30 to 60 seconds - Microsoft Q&A
• Unable to log into m365.cloud.microsoft, something went wrong - Microsoft Q&A