can't use new outlook

Question

can't use new outlook

Vivian Liang 20

I am trying switch to new outlook, but it always said something wrong as below:

UTC Date: [Moderator note: personal info removed]
Client Id: [Moderator note: personal info removed]
Session Id: [Moderator note: personal info removed]
Client Version: [Moderator note: personal info removed]
BootResult: fail
Back Filled Errors: None
err: Error: 440
esrc: StartupData
et: ServerError
estack: [Moderator note: personal info removed]
 
st: 440
efe: [Moderator note: personal info removed]

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Answer 1

Kristen-L 12,020 Microsoft External Staff Moderator

Hi @Vivian Liang,

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

From the details you’ve shared, it appears the new Outlook is failing during the StartupData phase with Error 440, which typically happens when the app is unable to load your account data from the service. This kind of error is usually related to an account or server‑side condition, rather than an issue with your local device.

Here are a few steps you can try to reset the new Outlook client:

1/ Hard‑close the new Outlook app

Close the new Outlook window
Press Ctrl + Shift + Esc to open Task Manager
Find Microsoft Outlook > select it > End task
Reopen the new Outlook app

2/ Clear New Outlook local cache

A. Delete the New Outlook settings file

Press Win + R
Paste: %localappdata%\Microsoft\olk
Delete: UserSettings.json
Launch New Outlook again

User's image

B. If still failing: delete the Olk + OneAuth folders

Close Outlook completely (Task Manager > End task)
Press Win + R, open: %localappdata%\Microsoft
Delete (or rename as backup) these folders:

Olk

OneAuth

Restart Windows
Open New Outlook and sign in again

3/ Uninstall & reinstall New Outlook

Uninstall New Outlook from device Settings

Go to Start > Settings > Apps > Installed apps
Select the app, then select More > Uninstall and confirm.

Reinstall New Outlook by:

Opening the Microsoft Store
Searching for Outlook for Windows
Selecting Install
Open Outlook and re‑add your email accounts

I hope this information helps. Please try the steps and let me know whether they resolve the issue. If the problem persists, we can work together to find a solution.

As other users will also search for information in this community, your vote can significantly help those with similar inquiries quickly locate the most relevant resources.

Thank you for your kindness and for contributing to the forum.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Vivian Liang 20 Reputation points

2026-03-10T15:43:40.7166667+00:00

{"SessionId":"af9d70b4-41d4-354c-b79b-ca7135d32678","Timestamp":1773157094255,"Error":"CONNECTFAILED undefined"}

I had followed your instructions and try again. it still showed the above information. it can't login with my business email, but it is good for Gmail.
Kristen-L 12,020 Reputation points Microsoft External Staff Moderator

2026-03-10T22:34:59.8866667+00:00
Hi @Vivian Liang,

Thank you for your response.

The error message indicates that the system is still unable to connect when you sign in with your business account, even though it works fine with your Gmail account. This usually means there may be a configuration issue, a permission restriction, or a sign‑in policy affecting your work email login.

At this point, please contact your IT administrator so they can review the issue from the backend. They may need to check:

Whether your business account has the correct permissions

Whether any conditional access, MFA, or security policies are blocking the connection

Whether the service you’re trying to log into is enabled for your organization

If your IT admin is unable to identify the cause, I recommend they open a support ticket in the Microsoft 365 Admin Center. This allows Microsoft Support to review your tenant settings and help troubleshoot authentication failures at a deeper level.

Please feel free to reach out if you have any questions.

Thank you for your understanding.

Warm regards.
Vivian Liang 20 Reputation points

2026-03-11T14:03:23.89+00:00

Thank you Kristen.

I will let them know.

very appreciate your reply.
Kristen-L 12,020 Reputation points Microsoft External Staff Moderator

2026-03-11T15:50:36+00:00

Hi @Vivian Liang,

Thank you for your message.

I appreciate your understanding. If you have any further questions or concerns, please feel free to reach out. I’ll be happy to assist further.

If you found my answer helpful, I’d really appreciate it if you could mark it as the Accepted Answer. This helps pin the solution to the top of the thread, making it easier for others in the community to find helpful guidance more quickly. Your contribution not only helps resolve your question but also supports other users who may be facing a similar situation.

Thank you very much, and I wish you a great day.

Answer 2

Error 440 during startup of new Outlook indicates a startup/launch problem in the new Outlook app, not in classic Outlook.

Use these concrete recovery steps:

Fully close new Outlook
1. Right-click Start → Task Manager.
2. If “Microsoft Outlook” is listed, select it → End task.
3. Close Task Manager.
Clear new Outlook local state This resets the new Outlook client-side data and often fixes “something went wrong” loops.
1. Close Outlook if open.
2. Press Windows+R.
3. Run:
```
      olk.exe --clearLocalState
```
4. After the command completes, start new Outlook again from Start.
5. When prompted, sign in and re-add accounts.
If the error persists, reset local Outlook/OneAuth caches
1. Close all Microsoft apps (Outlook, Teams, etc.).
2. Press Windows+R, type appdata, press Enter.
3. Go to Local > Microsoft.
4. Delete the folders:
  - Olk
  - OneAuth
5. Restart Windows.
6. Open new Outlook again and sign in.
If new Outlook still fails, reinstall it
1. Uninstall “new Outlook for Windows” from Start as described in the troubleshooting article.
2. Reinstall it either:
  - From classic Outlook using the Try the new Outlook toggle, or
  - From Microsoft Store using the provided Get new Outlook link.

If none of these steps resolve the 440 startup error, use classic Outlook or Outlook on the web temporarily and open a support case from the Microsoft 365 admin portal so support can review service-side issues for the account.

References:

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