Read time 10 minutes

Summary: Discover how to solve the frustrating “Cannot Expand the Folder” error when accessing email folders in MS Outlook. This error can occur due to various reasons, including corrupt OST files, server issues, or incorrect settings. To fix the problem, try basic troubleshooting steps such as restarting Outlook or repairing the mailbox. Still, if that does not work, the Kernel for OST to PST tool is highly recommended to recover corrupted OST files and access mailbox items without errors.

MS Outlook has become the to-go application for all professionals to prioritize all their email and data management needs. But it is also not immune to technical glitches. Many users have experienced trouble while opening certain PST folders. If you have similar issues where you cannot open or expand the folder in the Outlook application and do not get a way out of this, then reading this blog is a must for you.

We are going to explain the best solutions to fix this error and let you access the folder again to carry on with your work.

The error message that pops up is:

Cannot expand the folder. The set of folders cannot be opened.

Why does the error “Cannot expand the folder” occur?

This error is common in Outlook 2010 and later versions, to the extent that thousands of users have complained about it. It occurs when an Outlook user attempts to expand the shared folder, public folder, Address Book, or another secondary mailbox from the interface. Instead of expanding the respective folder, the error says:

Cannot expand the folder. The Set of Folders cannot be opened.
Cannot expand the folder. Microsoft Outlook cannot access the specified folder.

Let us know what reasons can be assumed for the occurrence of this error.

Reasons that are responsible for the “Cannot Expand the Folder” error

  • Exchange Cached mode is “ON.”
  • Interference of third-party add-ins
  • Corrupt Outlook profile
  • OST/PST file corruption
  • Microsoft Office application issue
  • Folder Visible permission is not set
Instant Solution

Try the automated tool Kernel for OST to PST Converter to Convert OST File to PST, EML, MSG, Office 365, and Exchange.

  • Backup OST data to PST
  • Search specific items within OST
  • Repair corrupt OST and NST files
Top manual solutions to fix “Cannot expand the folder” error

Try these simple solutions to fix or resolve the “Cannot expand the folder” error on your own.

Solution 1: Make the folder “Visible”
Solution 2: Disable the cached mode
Solution 3: Disable Microsoft Outlook Add-ins
Solution 4: Create a new Outlook profile
Solution 5: Repair the Outlook application
Solution 6: Repair the Outlook database files
Solution 7: Using the Microsoft Support & Recovery Assistant (MSRA) Tool
Here is the complete explanation of the above-mentioned solutions with their entire process.

Make the folder “Visible”

First, make sure that there are more subfolders than the limit. Earlier, the limit was 5000, but later, Microsoft increased the folder limit. Now, 5000 items per calendar folder and 100000 items per folder are allowed. Then check if the permission for the .Ost folder view is assigned or not.

  1. On the Outlook interface, right-click on the folder that is troubling you and click on the Properties option.
  2. Now, move to the Permissions tab and make sure that “Folder Visible” permission is assigned.
  3. If not, click on the Edit option and assign the same. Click OK to save the settings.
  4. Now, your problem may be resolved.
Disable the Cached Mode

Cached Exchange Mode saves a copy of the mailbox to the user’s computer, and this enables easy access to all the data. But when this mode is on, it may cause trouble in expanding the respective folder due to synchronization issues. It is suggested to disable the cached Exchange mode in Outlook in such a situation. Follow this process to do so-

  1. On your Outlook interface, navigate to File > Account Settings > Account Settings.
    Account Settings
  2. Under the Email section, on the Account Settings page, double click on the account causing the issue. Now, it will open the Change Account page. Here, under the Offline Settings section, unselect the Use Cached Exchange Mode option and click on Next to follow the further instructions and save this setting.
    Cached Exchange Mode
  3. Now, restart the Microsoft Outlook application and try to expand the folder.
Disable Microsoft Outlook add-ins

Conflicts with the third-party add-ins can affect the synchronization of the mailbox as well as the functioning of the application since they become roadblocks to a smoothly running function. Running the application in the Safe Mode might also help to resolve the issue. You can also try disabling the Outlook add-ins using the following procedure and then attempt to expand the problematic account folder.

  1. On the Microsoft Outlook application interface, click File > Info > Options.
    Microsoft Outlook application interface
  2. On the Outlook Options page, click Add-ins. Move to the right panel and then click on the Go option against Manage > COM Add-ins.COM Add-ins
  3. Now unselect the Add-ins and click on OK.
    unselect the Add-ins
  4. Restart the Microsoft Outlook application, and then try to expand folder again.
Repair the Outlook application

Due to some bugs, errors, or other issues, the application may also get corrupted. Taking it as a solid reason behind this issue, you can try performing an online repair on your Microsoft Office application suite. But before you begin with it, make sure you have a strong network speed to perform this repair. The procedure is as follows-

  1. Go to the Control Panel and click on the Programs and Features option.
  2. Move to the installed Microsoft Office program and right-click on it. Select the Change option from the drop-down list.
    Select the Change option
  3. Click Yes to continue.
  4. Now select the repair option as Quick Repair and click on the repair option
  5. Follow the next instructions to perform the repair.
  6. Once the repair is completed, try accessing the folder from the Outlook application.
Create a new Outlook profile

A corrupt Outlook profile is another major cause of many problems in Outlook, including this one. All Outlook users can anytime create a new Outlook profile and set it as the default one.This will give you a clean start, and the corruption-containing profile will be deleted for good.

Perform these steps to create a new Outlook profile-

  1. Go to the Control Panel and click on the Mail option.
  2. On the Mail Setup dialogue box, click on the Show Profiles option.Show Profiles
  3. Click Add to add a new profile. Then provide a name to the Outlook profile and click OK.add a new profile
  4. Now set this profile to your account by selecting the option saying Always use this profile and then selecting the account from the drop-down list. Then, click on OK.
    select Always use this profile
  5. Now launch the Outlook application with this new profile and check if the problem is resolved.
Repair the Outlook database file

The corrupt .ost file can be a reason for the error, but here you have an advantage that you can anytime recreate the OST file of your configured Exchange Server account. You just require opening the .ost file location from the Account Settings in Outlook and then deleting the problematic .ost file from there using the Delete option simply.

Select Delete option

The default location of the Microsoft Outlook .ost file is given as:


Then restarting the Outlook once would recreate a fresh .ost file without issues. It can resolve your issue if corrupt .ost is the problem.

For users who have corrupted or orphaned .ost files, we recommend the most efficient and secure Kernel OST to PST Converter, which readily recovers data from the corrupt, damaged, or orphaned offline .ost file and allows to save it to the PST file format and more destinations. This tool is suitable for all users, including beginners, and it will get the work done in a jiffy.Get complete information about the tool by visiting its official website.

Using the Microsoft Support & Recovery Assistant (MSRA) tool

To resolve the “Outlook cannot expand the folder” error in Microsoft Office applications, you need to download & install the Microsoft Support & Recovery Assistant (MSRA) tool on the affected system.

  1. Upon successful installation, launch the MSRA tool & accept the license agreement by clicking on the “I agree” button.launch the MSRA tool and accept the license agreement
  2. In the MSRA tool window, locate the “Outlook” option & select it, & then click on the “Next” button to proceed.locate the Outlook option
  3. Now select the “Outlook won’t start or other problems” option & tap on the “Next” button again.
  4. When prompted, confirm that you are experiencing the issue with Outlook by selecting “Yes,” & then proceed to the next step by clicking on the “Next” button.
  5. Follow the instructions on the MSRA wizard to diagnose & resolve the “Outlook cannot open set of folders” issue.
Folder limit

Microsoft Outlook allows you to create 1000 folders. If the number of subfolders exceeds the specified number, the folder will not expand. The limit is applicable to Microsoft Exchange accounts. There is a 500 folder limit for Outlook 2010, 2013, 2016, and 2019. In addition, no folder can contain more than 100,000 items. You might face performance issues in case these limits are exceeded. So, make sure you are within these prescribed limits.


To fix the “Cannot Expand the Folder” error, users must make sure that their mailbox is properly synced and configured with the necessary settings. If the issue persists, it could be due to corrupt or damaged OST files. In such cases, using a reliable OST to PST converter like Kernel for OST to PST is highly recommended. This efficient tool can easily convert OST files to PST without any issues with the integrity of user data. So, don’t let the error hamper your work efficiency and opt for this beneficial solution now.

Q- What does Cannot expand the folder in Outlook mean?

A- This error message indicates that there is not enough memory available to perform the operation, which can be caused due to different factors. It could be due to an issue with Outlook, or your computer is running low on memory and storage space. 

Q- What is the size limit for Outlook folders?

A- In Microsoft Outlook versions from 2010 to 2021 and Microsoft 365, the size limit for Outlook folders is set to 50GB. But it is not recommended to exceed this limit due to potential performance concerns.

Kernel for OST to PST