Article ID: 2798988 - View products that this article applies to.
When you try to open Outlook Web App in Microsoft Office 365, you receive the following error message:
There was a problem opening your mailbox. You may have already signed in to Outlook Web App on a different browser tab. If so, close this tab and return to the other tab. If that doesn't work, you can try:
- Closing your browser window and signing in again.
- Deleting cookies from your browser and signing in again.
This issue occurs when the following conditions are true:
Use one of the following methods, as appropriate for your situation.
Still need help? Go to the Office 365 Community