I encountered problems using Outlook, both the new Outlook and Outlook on the web.

Dear @Thaninee Manghirun,

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

Based on your description and the screenshot, Outlook on the web is showing a generic “Something went wrong” error page.

This issue is typically caused by a temporary session or browser-related problem rather than a mailbox issue. Please confirm me some information as:

Can you log in to office.com successfully?

Does the issue happen on all devices or only one?

In the meantime, to resolve it, you can try the following:

Refresh the page (Ctrl + F5) or click Refresh the application.

Sign in using an InPrivate/Incognito browser session.

Clear your browser cache and cookies, then try again.

Test with a different browser or device.

Please update for me if the issue still persists if you have tried all the methods above.

Looking forward to your update.

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Hi Thaninee Manghirun

I understand you’re unable to access your mailbox in both new Outlook and Outlook on the web. Those details may suggest a service-side transient mailbox/storage condition (“server too busy / transient failure”). Are you signing in with a personal Outlook.com/Hotmail account, or a work/school Microsoft 365 account?

I would love to hear from you soon. Have a lovely day!

The error details in the screenshot show a transient Exchange Online storage/server issue (StorageTransientException, MapiExceptionRpcServerTooBusy, HTTP status 500). This is a backend problem rather than a client configuration problem in new Outlook or Outlook on the web.

Because this is a service-side condition, local troubleshooting (reinstalling Outlook, clearing cache, trying different browsers, etc.) will not permanently fix it. The recommended actions are:

1. Use Outlook on the web or new Outlook again after some time, as transient storage and “server too busy” conditions are typically auto‑recovered by the service.
2. If the problem persists and you are in an organization (Microsoft 365 tenant), the Microsoft 365 admin should open a support case from the Microsoft 365 Admin portal so Exchange Online support can investigate and mitigate at the service level. This is similar to other Exchange Online issues where only service-side changes resolve the problem.
3. As a temporary workaround while the issue is being investigated, continue using whichever Outlook endpoint still works (for example, classic Outlook for Windows if it connects successfully) until the backend error is cleared.

References:

• 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."