How to Fix Outlook 'Cannot Expand Folder' Errors When Accessing Shared Mailboxes in Microsoft 365

Summary

This guide helps you troubleshoot and resolve: How to Fix Outlook 'Cannot Expand Folder' Errors When Accessing Shared Mailboxes in Microsoft 365. Follow the steps below to fix the issue.

Common Causes

Shared mailboxes allow multiple users to send and receive email from a single address, such as [email protected] or [email protected]. If Outlook displays a “Cannot expand folder” error when you try to access a shared mailbox, it usually means your permissions are not syncing correctly or your Outlook profile needs refreshing. This guide walks Australian small business users through the most effective fixes for Outlook desktop.

Quick Fix Steps

1. Restart Outlook and wait a few minutes for shared folders to synchronise.
2. Confirm with your Microsoft 365 administrator that you have been granted Full Access or Read permissions to the shared mailbox.
3. Check that you are using the Outlook desktop app, not Outlook on the web, as shared mailbox behaviour differs between clients.

Detailed Instructions

Method 1: Remove and Re-add the Shared Mailbox

1. Open Outlook and select File from the top menu.
2. Choose Account Settings, then select Account Settings again from the dropdown.
3. On the Email tab, select your primary Microsoft 365 account and click Change.
4. Click More Settings, then open the Advanced tab.
5. Under Open these additional mailboxes, select the shared mailbox causing the error and click Remove.
6. Click Add, type the shared mailbox email address, and click OK.
7. Click OK to close the dialog boxes, then click Next, Finish, and Close.
8. Restart Outlook and check if the shared mailbox folders now expand correctly.

Method 2: Clear Outlook Cached Mode Data

1. Select File, then Account Settings > Account Settings.
2. Select your Exchange account and click Change.
3. Under Download email for the past, move the slider to All.
4. Uncheck Use Cached Exchange Mode, click Next, then Finish.
5. Restart Outlook.
6. Once folders load correctly, repeat the steps above and re-enable Use Cached Exchange Mode if you prefer offline access.

Method 3: Repair Your Outlook Profile

1. Close Outlook completely.
2. Open Control Panel and select Mail (Microsoft Outlook).
3. Click Show Profiles, select your profile, and click Properties.
4. Click Email Accounts, select your Microsoft 365 account, and click Repair.
5. Follow the prompts to complete the repair, then restart Outlook.

Troubleshooting

Error persists after re-adding the mailbox

If the folder still will not expand, your organisation’s administrator may need to verify that the correct permissions are assigned in the Microsoft 365 admin centre. Ask them to check that your user account has at least Folder Visible permission on the root mailbox, plus Author, Editor, or Owner permissions on the specific folders you need to access.

Shared mailbox appears but folders are empty

This often indicates a synchronisation delay. Leave Outlook open and connected to the internet for at least 30 minutes. If folders remain empty, try toggling Cached Exchange Mode off and back on as described in Method 2.

Only one user is affected

If other colleagues can open the same shared mailbox without issue, the problem is local to your Outlook profile or computer. Creating a new Outlook profile via Control Panel > Mail > Show Profiles > Add can resolve persistent client-side corruption.

If none of these steps resolve the issue, your mailbox permissions may need to be reset by your administrator. Open a Ticket with 220 Internet Services and include the exact error message and the shared mailbox email address.

Related articles:

• Setting Up an Email Account in Outlook (POP/IMAP/Exchange)
• Managing Email Signatures in Outlook
• Troubleshooting Outlook Send/Receive Errors
• Backing Up and Restoring Outlook Data Files (.pst/.ost)
• Organizing Emails with Rules and Alerts in Outlook
• Using Outlook Calendar and Scheduling Meetings

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