Subject: Technical Escalation: Persistent Error 440 / StartupData Failure

Question

Problem Description: I am unable to log in to my Outlook Web App (OWA) and my account has stopped syncing to my mobile devices. While my Outlook desktop application is still working, any attempt to sign in via a web browser or on my phone results in a crash during the startup process.

The Error I am Seeing: I have captured the following error details from the login screen:

• Error Code: 440
• esrc: StartupData
• et: ServerError
• BootResult: fail
• Client Version: [Moderator Note: Personal Info Removed]

Troubleshooting I Have Already Done: I have already tried clearing my browser cache and using Incognito/Private mode across several different browsers and networks. The results are always the same. Because this error happens during the "StartupData" phase, I believe this is a server-side issue with my account and not a problem with my local computer or phone.

Our Technical Theory: I suspect an Identity Conflict (Orphaned Account). Since my email is on a custom domain ([Moderator Note: Personal Info Removed]), it appears there may be a collision between a Personal Microsoft identity and a legacy Work or School identity. This seems to be causing a "handshake" failure that prevents my session from starting.

My Request for Investigation:

1. Reconcile My Identity: Can you check the backend for my email address to see if there is a "ghost" or legacy organizational account conflicting with my personal account? When I login to the 'Work or School' account, the email appears as [Moderator Note: Personal Info Removed]@outlook.com
2. Verify Mailbox Health: Please check if my OWA mailbox features are healthy and that my "StartupData" attributes are correctly configured on your end.
3. Alias Check: If there is an identity collision, please let us know if I need to temporarily set a new Primary Alias (like an @outlook.com address) to fix the domain conflict.

I can provide a screenshot of the full error page and Session ID if needed.

Answer 1

Hi LG,

Thank you for reaching out to Microsoft Q&A forum.

Based on the timeline in your screenshot, the incident you reported on the 14th aligns with an update Microsoft released on the 10th. That update temporarily affected the ability to sign in to Outlook.com using certain browsers.

Microsoft has already reverted the change and confirmed that the service has been fully restored.

Please try signing in to OWA again. If you still cannot access it, you can try using another browser.

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Answer 2

Below is a screenshot when I try to login. This is a personal subscription, not a work or school account. Microsoft should be able to triage this.