I am unable to login into new outlook app as well as web login

Question

UTC Date: 2025-11-15T15:32:15.393Z
Client Id: Remove PII
Session Id: Remove PII
Client Version: Remove PII
BootResult: fail
Back Filled Errors: None
err: Error: 440
esrc: StartupData
et: ServerError
estack: Error: 440
    at Object.w [as createStatusErrorMessage]
st: 440

Moved from: Microsoft 365 and Office | Office Online Server

Answer 1

I am unable to receive or sent mails in new outlook app

Answer 2

Dear @Binoy R,

Thank you for posting your question in the Microsoft Q&A forum.

Before giving you the best solution, could you please confirm these questions below to help me diagnose the issue more effectively: 

• Is this a work/school account (from your organization) and do other Microsoft 365 apps (e.g., portal.office.com or Teams on the web) sign in successfully on the same device/network?
• Does your account use a personal account (@outlook.com/@hotmail.com email), or is it a work/school account (e.g., @company.com)? 
• If you are using business account, Are you the admin in your company? If yes, are you the only admin or there are other admins in your company?  

In Outlook on the web (OWA)/New Outlook startup, 440 commonly indicates a session/authentication cookie problem or a sign‑in handshake that didn’t complete (expired/invalid cookie, blocked third‑party storage, network rewriting, or a protection policy interrupting token issuance). Therefore, here are some steps I recommend you check and try again:

Step 1: Clear Cache

• Private window: Edge/Chrome: Ctrl+Shift+N and sign in.
• Clear site data for Outlook (avoid clearing all history): Edge/Chrome: go to edge://settings/siteData or chrome://settings/siteData > search office.com, live.com, microsoftonline.com, outlook.office.com > Remove each > Then fully close the browser (all windows) and retry.

Disable extensions temporarily (ad‑blockers/privacy tools can block cookies or script resources from *.microsoft.com / *.office.com / *.office365.com / *.msauth.net / *.msftauth.net).

Step 2: Network test

Turn off VPN/proxy/Zscaler and try a different network (mobile hotspot) to rule out SSL inspection or tenant‑restriction proxies.

If you’re on a corporate network with SSL inspection, ensure Microsoft 365 endpoints are excluded from break/inspect.

Step 3: Manually clear the cache in Outlook

Before attempting to clear the cache in Outlook, first try to remove the sideloaded add-in using the steps outlined in Sideload Outlook add-ins for testing.

If this add-in removal doesn't work, then delete the contents of the Wef folder as noted for Excel, Word, and PowerPoint in Manually clear the cache in Excel, Word, and PowerPoint.

If your Outlook add-in uses the Unified manifest for Microsoft 365, also delete the following folder: %userprofile%\AppData\Local\Microsoft\Outlook\HubAppFileCache

To clear the cache in new Outlook on Windows, perform the following steps.

• Close the Outlook client if it's open.
• From a command line, run the following: command line: olk.exe --devtools
• This opens the new Outlook on Windows client and an instance of the Microsoft Edge DevTools.
• In the Microsoft Edge DevTools window, select the Network tab.
• Select and hold (or right-click) anywhere in the Requests table. Then, select Clear browser cache.
• For reference: Manually clear the cache in Outlook

Step 4: Clear Local State Outlook

Close the new Outlook, open the Run command (Windows key + R) and type or paste this command line. Note, there is a space before the two dashes -- and yes, you use two dashes.

olk.exe --clearLocalState

Just like this:

This deletes your profile and when you open the new Outlook, you'll need to add your account. Add additional accounts from the Settings dialog.

However, the error code 440 with the source "StartupData" and type "ServerError" typically points to a problem on the server side rather than something caused by your browser or device. Although trying clearing cache and switching browsers are good initial steps this particular error may be related to a corrupted mailbox or a misconfiguration in your account settings on the server.

According to updated guidance from Microsoft one effective resolution is to sign out of all sessions across devices via account.microsoft.com then reauthenticate using your credentials and complete any required multi-factor authentication. This refreshes your session tokens and can help resolve authentication-related issues that trigger error 440.

Additionally, it's worth checking that your device’s date and time settings are accurate as mismatches can interfere with secure connections.

If you're using a work or school account collaborating with your IT administrator to verify your account’s sync status in Exchange Online or Active Directory is also recommended. They can check for any mailbox corruption, policy restrictions or service advisories that may be affecting your access. For reference: How do I find my Microsoft 365 admin?

I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this.

Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.

Thank you for your patience and your understanding. If you have any questions, please feel free to reach out.

I'm looking forward for your reply.

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