Outlook will not open

The BootResult: network and StartupData: Failed to fetch details indicate that Outlook.com could not retrieve the data needed to start, so remove its browser site data first and then isolate browser, network, and Microsoft-service causes.

1. Remove only Outlook/Microsoft site data

This avoids deleting cookies for every website. Clearing the affected cookies was the accepted recommendation for a similar Outlook web StartupData error—not a confirmed outcome for every case.^1^

Microsoft Edge

1. Open Outlook.com.
2. Select the icon immediately to the left of the address in the address bar.
3. Select Cookies and site data → Manage cookies and site data.
4. Delete entries associated with Outlook, Live, and Microsoft sign-in.
5. Close all Edge windows, reopen Edge, and sign in again.

Google Chrome

1. Open Outlook.com.
2. Select the site-controls icon to the left of the address.
3. Select Cookies and site data → Manage on-device site data.
4. Delete the Outlook, Live, and Microsoft sign-in entries.
5. Close all Chrome windows, reopen Chrome, and sign in again.

2. Test a clean browser session

1. Update and use a supported browser: current Edge, Chrome, or Firefox on Windows; current Edge, Chrome, Firefox, or Safari 16 or later on macOS.^2^
2. Open an InPrivate or Incognito window and test Outlook.
3. If it works there, return to the regular window and disable extensions individually:
   • Edge: Extensions → Manage extensions
   • Chrome: Menu → Extensions → Manage extensions
4. Start with ad blockers, tracker blockers, and script-filtering extensions. Microsoft specifically notes that AdBlock and uBlock can cause Outlook.com loading problems.^2^

3. Separate a network problem from an account problem

1. Disconnect any VPN or proxy temporarily. The exact path depends on the operating system; on Windows it is normally Settings → Network & internet → VPN or Proxy.
2. Connect the device to another network, preferably a phone’s cellular hotspot, and retry.
3. If security software includes HTTPS scanning or web protection, first prefer the clean-browser test above. If it must be disabled for diagnosis, do so only briefly, visit only the official Outlook.com site, and re-enable it immediately afterward.
4. Check Microsoft’s public service-health page for an Outlook or Microsoft 365 incident.^3^

A reported incident should be allowed to clear before making account changes. A green status page does not exclude a mailbox-specific Microsoft-side problem.

4. Escalate if the failure follows the account

If Outlook fails with the same StartupData: Failed to fetch details in:

• multiple supported browsers,
• another device, and
• another network such as cellular data,

the remaining evidence points away from browser cache and the original network. Similar failures reproduced across devices and networks have been treated as server- or mailbox-side issues.^4^ There is no documented user-side mailbox repair to run.

For a personal Microsoft 365/Outlook.com account:

• If the Microsoft account itself cannot sign in, use Microsoft’s personal-account sign-in helper; Outlook.com support cannot change account details or bypass sign-in protection.^5^
• If the account signs in elsewhere but the mailbox will not open, contact Microsoft consumer support and include:
  • the complete error text,
  • UTC date,
  • Client ID and Session ID,
  • Client Version,
  • BootResult: network,
  • esrc: StartupData,
  • confirmation that it fails on multiple browsers, devices, and networks.^6^

Do not post the Client ID or Session ID publicly; provide them only in the private support case. Repairing the installed Office suite or creating a desktop Outlook profile is not applicable to this browser startup failure.

References

1. Getting this error when trying to log into outlook on browser: - Microsoft Q&A
2. Supported browsers for Outlook on the web and Outlook.com | Microsoft Support
3. Service Health Status - Microsoft
4. My Outlook.com mailbox is inaccessible across all clients. - Microsoft Q&A
5. How to get support for Outlook.com | Microsoft Support
6. Contact Microsoft customer support | Microsoft Support