Troubleshooting 'Cannot Open Folder' Error in Office 365 Outlook

If you are experiencing issues with your Office 365 Outlook account, specifically the 'Cannot open folder' error, there are several troubleshooting steps you can take to resolve the issue.

The first step is to check if the cache mode is enabled. To do this, go to File > Options > Advanced and look for the 'Use Cached Exchange Mode' option. If it's checked, uncheck it and save your settings. Closing and reopening Outlook will force it to re-sync and download folders and emails again.

Another possible cause of the error is add-ins. If you have installed any add-ins in your Microsoft Outlook account, one or more of them may be causing a conflict resulting in the 'Cannot open folder' error. To eliminate this possibility, open Outlook in Safe Mode by holding down the Ctrl key while launching the application. This will disable all add-ins and allow you to test if the issue persists.

If the issue still occurs in Safe Mode, it's likely that one of your add-ins is causing the problem. You can try disabling each add-in individually to identify which one is responsible for the error.

Another possible cause of the 'Cannot open folder' error is a limitation imposed by Microsoft Outlook. According to Microsoft notes, if you have more than 1000 folders in your account or more than 100,000 items per folder, you may face performance issues and the folder will not expand. This limit applies specifically to Microsoft Exchange accounts.

To check if this is the case, go to File > Account Settings > Account Settings and select the email ID that is throwing the 'Cannot expand folder' error. You will see a list of all your email accounts, including shared mailboxes. If the issue occurs on an Exchange account or in a shared mailbox, turning off cache mode could help resolve the problem.

In some cases, simply searching for the standalone Outlook app or Microsoft Office suite version can help resolve the issue. If you have installed one of these versions, uninstalling it may resolve the problem.

If none of these steps resolve the issue, you can try using the Control Panel to uninstall any recently installed add-ins or applications that may be causing a conflict with your Outlook account.

By following these troubleshooting steps, you should be able to resolve the 'Cannot open folder' error in Office 365 Outlook and get back to using your email account normally.

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