Fixed: 'Set of Folders Cannot Be Opened' Error in Outlook Shared Mailbox

Introduction

The "Set of Folders Cannot Be Opened" error is a common issue that occurs when users attempt to access shared mailboxes in Outlook. This error prevents Outlook from loading mailbox folders properly, disrupting normal email operations and causing significant inconvenience.

Other Situations Where This Error Usually Also Appear

• When starting Outlook
• After a Windows or Office update
• After migrating Outlook data or profiles

Why Does Outlook Say Cannot Open Set of Folders?

Outlook displays the error "Cannot open the set of folders" when it fails to load your mailbox, profile, or required data files during startup. This usually indicates a configuration or data-related problem rather than an Outlook bug itself.

Corrupted Outlook Profile

A damaged profile is the most frequent cause. If Outlook cannot read profile settings, it will stop during launch.

• Damaged PST or OST File

Corruption in Outlook data files prevents mailbox folders from loading properly.

• Incorrect Shared Mailbox Permissions

When accessing a shared mailbox, missing or incomplete permissions can trigger this error.

• Navigation Pane Configuration Issues

Corrupted navigation pane settings may block Outlook from opening folder structures.

• Incompatible or Faulty Add-ins

Some Outlook add-ins can interfere with startup and folder loading.

• Outdated or Incomplete Outlook Updates

Running an outdated version of Outlook may cause compatibility issues with Exchange or Microsoft 365.

• Incorrect Account or Server Settings

Wrong Exchange, IMAP, or Microsoft 365 configuration can prevent Outlook from connecting to the mailbox.

Solutions to Outlook "Set of Folders Cannot Be Opened"Error

If you see the "Set of folders cannot be opened" error in Outlook, it means Outlook is having trouble loading your mailbox or a shared mailbox. Don’t worry—this is a common issue and can usually be fixed by following the steps below.

★First to Try: Restart Outlook or Your Computer

Sometimes, the error is caused by a temporary glitch in Outlook or your system. A simple restart can often fix minor issues without any complicated steps.

1. Open Outlook in Safe Mode

Safe Mode starts Outlook without add-ins, helping identify whether an add-in is causing the issue.

Step 1. Close Outlook completely.

Step 2. Press Windows + R on your keyboard.Type "outlook.exe /safe" and click "OK".

Step 3. Select your profile if prompted.

If Outlook opens normally, an add-in is likely the cause.If so, you can skip to Method 3 to disable add-ins.

2. Reset the Navigation Pane

The navigation pane in Outlook is the panel on the left where you see your folders (Inbox, Sent, Calendar, etc.). Sometimes this panel can become corrupted, preventing Outlook from opening folders correctly. Resetting it restores the default layout without affecting your emails.

Close Outlook.Press Windows + R. Type "outlook.exe /resetnavpane" and press Enter. Outlook will open with the default folder view. Your previous folder layout and shortcuts will be reset. Then try accessing your mailbox and shared folders to check if the "Set of Folders Cannot Be Opened" error is gone.

3. Disable Problematic Add-ins

Add-ins are small programs that add extra features to Outlook, such as calendar tools or email plugins. Sometimes, faulty or outdated add-ins can prevent Outlook from starting properly or cause the "Set of folders cannot be opened"error. Disabling them helps identify the culprit and restores normal Outlook functionality.

Step 1. Open Outlook (use Safe Mode if needed).Go to "File → Options".

Step 2. Access to "Add-ins" tab.At the bottom, select "COM Add-ins" and click "Go".

Step 3. Uncheck all add-ins and click "OK".

Restart Outlook and enable add-ins one at a time if neededto figure out which one is causing the problem.

4. Update or Repair Microsoft Outlook

Outlook may not open or may show errors if program files are corrupted or outdated. Updating or repairing Outlook restores missing or damaged files and ensures compatibility with your mailbox and system.

Step 1. Open "Control Panel → Programs → Programs and Features".

Step 2. Select Microsoft Office / Microsoft 365.Click "Change".

Step 3. Choose "Quick Repair" first. If the issue continues, run "Online Repair".

5. Create a New Outlook Profile

A corrupted Outlook profile is a common cause of the "Set of folders cannot be opened" error. Creating a new profile gives Outlook a fresh configuration without affecting your emails stored on the server (Exchange, Office 365, or IMAP accounts).

Step 1. Make sure Outlook is not running in the background. Check Task Manager for any OUTLOOK.EXE processes and end them if needed.

Step 2. Open Control Paneland click Mail (Microsoft Outlook). If you don’t see Mail, change View by: to Small icons.

Step 3. In the Mail Setup window, click "Show Profiles".

Step 4. Click "Add" to create a new profile.Set up the new profileand follow the prompts to add your email account(s).

Outlook will attempt to configure settings automatically. You may need your email address and password.Set the new profile as default. Launch Outlook and check if your mailbox and folders open normally.

6. Repair Outlook Data Files (PST or OST)

Outlook stores your emails, calendar, and contacts in data files called PST (for POP/IMAP accounts) or OST (for Exchange/Office 365 accounts). If these files become corrupted, Outlook may fail to open or show the error. Repairing them fixes internal errors without deleting your data.

Step 1. Locate the Inbox Repair Tool (SCANPST.EXE). Its location depends on your Office version, for example:

C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE (Office 2016/2019/365)

C:\Program Files (x86)\Microsoft Office\Office15\SCANPST.EXE (Office 2013)

Alternatively, you can press "Windows + S", type "SCANPST.EXE", and search.

Step 2. Open "SCANPST.EXE" and select your data file:

Step 3. Click "Browse…" and navigate to your PST or OST file.

Step 4. Click "Start" to scan the file.The tool will detect errors in the data file.

Step 5. After scanning, click "Repair" to fix detected issues.

Open Outlook normally and check if your mailbox and folders are accessible.

7. Disable Cached Exchange Mode

Cached Exchange Mode stores a local copy of your mailbox on your computer to improve performance. However, sometimes it can cause synchronization issues that prevent Outlook from opening folders properly. Disabling it forces Outlook to connect directly to the server, which can help resolve the "Set of folders cannot be opened"error.

Step 1. Access Outlook "Email Accounts" from Control Panel (refer to solution 5).

Step 2. Select your email account and click "Change".

Step 3. Uncheck "Use Cached Exchange Mode". Click "Next → Finish", then restart Outlook.

8. Check Shared Mailbox Permissions

If you are trying to access a shared mailbox, missing or incorrect permissions can prevent Outlook from opening it, causing the error. Ensuring proper access rights is essential for shared mailboxes to function correctly.

Step 1: Log in to the Microsoft 365 Admin Center in a web browser and go to "Teams & Groups → Shared mailboxes"to locate the shared mailbox that is causing issues.

Step 2: Check the "Mailbox permissions"to make sure your account has "Full Access" (and "Send As"if needed). If the permissions are missing, add or adjust them and save the changes.

Step 3: Close and reopen Outlook, then try accessing the shared mailbox again. The error should be resolved once proper permissions are applied.

9. Check the Shared Mailbox License

If a shared mailbox is assigned the wrong license,anypotential conflicts or access issues can occur. So, we also need to ensureOutlook can connect and synchronize the mailbox correctly.

Step 1: Open a web browser and go to https://portal.office.com, then log in with your admin account and navigate to Users → Active Users.

Step 2: Find and click on the shared mailbox you want to check, then open the Product licenses section to see if any licenses are assigned.

Make sure the shared mailbox is not assigned an Exchange Online license unless specifically required, as unnecessary licenses can sometimes cause access or synchronization issues. After verifying, close Outlook and try opening the mailbox again.

Summary

The "Set of Folders Cannot Be Opened" error in Outlook is a common but usually solvable issue. Regularly maintaining Outlook, keeping it updated, and ensuring correct mailbox configurations can help prevent this error from recurring in the future.