Unable to expand the folder, Client operation failed – Outlook error

While accessing mailbox folders, expanding a shared folder, or accessing some secondary mailbox, you may encounter the “Unable to expand the folder, Client operation failed” error. Usually, error messages like “Cannot expand the folder” or “Unable to expand the folder” occur on Outlook Exchange accounts. If you see this error message in Outlook, you can try the solutions provided in this post.

Unable to expand the folder, the Client operation failed

Related Post: Sorry, we’re having trouble opening this item in Outlook

The following solutions may help you fix this problem in Outlook:

• Check the status of the Cached Exchange Mode
• Grant Full Access permission to the mailbox
• Troubleshoot Outlook in Safe Mode
• Repair corrupted OST and PST files
• Use the Microsoft Support and Recovery Assistant tool

Let’s see all these solutions in detail.

Check the status of the Cached Exchange Mode

Cached Exchange Mode enables a copy of your mailbox to be saved on your computer, providing quicker access to your data and more regular updates with the Microsoft Exchange server.

You might be experiencing this issue because of the disabled Cached Exchange Mode. To fix this, check if Cached Exchange Mode is enabled or not. If it’s disabled, enable it. If it’s already enabled, disable it and then enable it again.

• Open Microsoft Outlook.
• Go to “File > Account Settings > Account Settings.”
• Select Exchange or Microsoft 365 and click Change.
• Under the Offline Settings, see whether the “Use Cached Exchange Mode” checkbox is selected or not. If not, select it. If the checkbox is already selected, deselect it and exit Outlook. Now, start Outlook again and turn this feature on.

Grant Full Access permission to the mailbox

Another cause of this problem is the permission issue. In Outlook Exchange and Outlook 365, you can make delegates open and read the email messages of another account assigned to them. The delegates will get the “Unable to expand the folder” error message while expanding the folders of the shared inbox if Full Access permission is not granted to the mailbox.

The Resolution: To resolve the issue, you need to grant Full Access permission to the mailbox. This will allow the delegates to open the mailbox and view, add, and remove the contents of the mailbox. However, it will not allow the delegates to send messages from the given mailbox. Note that if you assign Full Access permission to a mailbox that is hidden from the address list, the delegates will not be able to open that mailbox.

The following steps will help you:

• Log into your Exchange Admin Center.
• Open the list of Mailboxes and select the mailbox, the permission of which you want to change.
• Now, click on the Manage permission delegation link under the Mailbox permissions.
• Click on the Edit button next to Read and manage.
• Click Add permissions.
• You will see the list of users along with their email IDs. Select the user to which you want to assign the Full Access permission of the mailbox.
• Click Save.

Troubleshoot Outlook in Safe Mode

Another issue could be due to a conflicting add-in. To check if this might be the case for you, open Outlook in Safe Mode and see if you can expand the folders or not. In the Safe Mode, add-ins remain disabled. If the issue does not occur in the Safe Mode, then the problem is likely with a certain add-in.

To find out which add-in is causing the problem, close Outlook in Safe Mode and open it in Normal Mode. Then follow the instructions below:

• Go to “File > Options.”
• Click Add-Ins on the left side.
• Select COM Add-ins in the Manage drop-down and click Go.
• Uncheck one of the checkboxes and click OK. This action will disable that particular add-in.
• Check if the issue appears.

To identify the problematic add-in, launch Outlook in normal mode and close it in Safe Mode. Now, follow the steps written below:

Why can’t I expand the folder pane in Outlook?

One of the causes of a delegate not being able to open and read the emails in a shared mailbox is a permission issue. To fix this, the shared mailbox should have Full Access permission. Another possible cause is if the Cached Exchange Mode is disabled or turned off. You can also try launching Outlook in the Safe Mode to check for conflicting add-ins.

How do you fix Cannot expand the folder, the set of folders cannot be opened, and the attempt to log on to Microsoft Exchange has failed?

If you get the “The set of folders cannot be opened” error in Outlook, you might be able to fix it by resetting the Navigation Pane in Outlook, disabling Outlook add-ins, making your mailbox smaller, or removing and re-adding your account.