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

While accessing the 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, Client operation failed

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

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

Let’s see all these solutions in detail.

1] Check the status of the Cached Exchange Mode

The Cached Exchange Mode provides users with a better experience when they use an Exchange account. When this mode is enabled, a copy of your mailbox is saved on your computer. This not only lets you quickly access your data but also updates data frequently with the server that runs Microsoft Exchange.

You might be experiencing this issue because of the disabled Cached Exchange Mode. Check if this mode is enabled or not. If you find it disabled, enable it. If it is already enabled, disable it and then enable it again. The following instructions will guide you on this:

1. Open Microsoft Outlook.
2. Go to “File > Account Settings > Account Settings.”
3. Select Exchange or Microsoft 365 and click Change.
4. 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.

Now, check if you can expand the folders or not.

2] 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.

To resolve this issue, you have to grant Full Access permission to the mailbox. Granting Full Access permission to the mailbox will allow the delegates to open the mailbox and view, add, and remove the contents of the mailbox. But it does not allow the delegates to send the messages from the given mailbox. Do note that, if you assign the Full Access permission to the mailbox that is hidden from the address list, the delegates will not be able to open that mailbox.

The following steps will help you:

1. Log into your Exchange Admin Center.
2. Open the list of Mailboxes and select the mailbox, the permission of which you want to change.
3. Now, click on the Manage permission delegation link under the Mailbox permissions.
4. Click on the Edit button next to Read and manage.
5. Click Add permissions.
6. 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.
7. Click Save.

3] Troubleshoot Outlook in Safe Mode

Another cause of the problem is a conflicting add-in. To check if this is the case with 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, you have to identify the problematic add-in.

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

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

Repeat the above steps until you find the problematic add-in. Once you find it, remove it from Outlook.

4] Repair corrupted OST and PST files

If the OST and PST files in Outlook get corrupted, you will experience several issues in Outlook. To fix the problem, repair the corrupted OST and PST files.

5] Use the Microsoft Support and Recovery Assistant tool

The Microsoft Support and Recovery Assistant tool runs some tests on your system to find out the cause of the problem and offers the best solution to fix the problem. You can use this tool to fix Microsoft Office, Microsoft Office 365, and Outlook problems. The tool is available on the official website of Microsoft for free. Download and use this tool and see if it helps.

Read: Outlook Cannot send this meeting request.

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

One of the causes of being unable to expand the folder in Outlook is the permission issue. It is necessary that the shared mailbox should have Full Access permission so that the delegate will be able to open it and read the emails. Apart from that, this problem also occurs if the Cached Exchange Mode is disabled or turned off. You should also check if there is a conflicting add-in by launching Outlook in the Safe Mode.

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

If you see the “The set of folders cannot be opened” error in Outlook, you can try some fixes, like resetting the Navigation Pane in Outlook, disabling your Outlook add-ins, decreasing the size of your mailbox, removing and adding your account again, etc.

Hope this helps.

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