How to Fix Outlook Error 8004010F When Adding a Shared Mailbox

Error 8004010F appears in Outlook when you try to open a shared mailbox that you have already added to your profile. The error usually reads: Cannot open your default e-mail folders. The information store could not be opened. The root cause is a corrupted or outdated cached copy of the shared mailbox in your local Outlook data file. This article explains why the error occurs and provides three tested methods to resolve it without deleting your main mailbox profile.

You do not need administrator rights for the first two fixes. The third fix requires temporary access to the Exchange admin center or help from your IT team. Follow the steps in order because the simplest repair often works.

Why Outlook Error 8004010F Occurs with Shared Mailboxes

Outlook stores a local copy of every shared mailbox you add when Cached Exchange Mode is enabled. This copy is saved in an Offline Storage Table file (.ost) on your computer. Over time, the .ost file for a shared mailbox can become corrupted due to an unexpected shutdown, a network interruption during synchronization, or a conflict after a Windows Update.

When Outlook tries to open the shared mailbox, it reads the corrupted .ost file first. The corrupted data prevents the connection to the Exchange server, and Outlook returns error 8004010F. The error does not mean your mailbox or the shared mailbox is damaged on the server. It only means the local cached copy is unreadable.

How Shared Mailbox Caching Works

By default, Outlook 2016, Outlook 2019, Outlook 2021, and Microsoft 365 Outlook use Cached Exchange Mode. When you add a shared mailbox through File > Account Settings > Change > More Settings > Advanced > Add, Outlook downloads a full copy of that mailbox to your local drive. The cached copy allows fast access and offline availability. If the .ost file for that shared mailbox becomes corrupt, the error appears every time Outlook attempts to sync or open it.

Why the Error Does Not Affect Your Primary Mailbox

Your primary mailbox has its own .ost file. Error 8004010F is specific to the shared mailbox’s .ost file. This is why your primary mailbox continues to work normally even when the error appears. The fix targets only the shared mailbox’s cached data, not your main profile.

Step 1: Remove and Re-add the Shared Mailbox

This method removes the corrupted .ost file for the shared mailbox and creates a fresh copy from the server.

1. Open Account Settings in Outlook
   Click File > Info > Account Settings > Account Settings. Select your Exchange account and click Change.
2. Locate the shared mailbox entry
   In the Change Account window, click More Settings > Advanced. Under Open these additional mailboxes, find the shared mailbox that shows error 8004010F.
3. Remove the shared mailbox
   Select the shared mailbox name and click Remove. Click OK to close all dialog boxes. Restart Outlook.
4. Re-add the shared mailbox
   Go back to File > Account Settings > Account Settings > Change > More Settings > Advanced. Under Open these additional mailboxes, click Add. Type the shared mailbox name or email address and click OK. Click Apply, then OK. Restart Outlook.

Outlook now downloads a fresh .ost file for the shared mailbox. The error should no longer appear.

Step 2: Disable Cached Exchange Mode for the Shared Mailbox

If removing and re-adding the shared mailbox does not work, turn off caching for that mailbox. This forces Outlook to open the mailbox directly from the server every time.

1. Open the Exchange account settings
   Click File > Account Settings > Account Settings. Select your Exchange account and click Change.
2. Turn off Cached Exchange Mode
   Uncheck Use Cached Exchange Mode. Click Next, then Finish. Restart Outlook.
3. Add the shared mailbox again
   Go to File > Account Settings > Account Settings > Change > More Settings > Advanced. Under Open these additional mailboxes, click Add. Type the shared mailbox name and click OK. Click Apply, then OK. Restart Outlook.
4. Re-enable Cached Exchange Mode (optional)
   If you want caching for your primary mailbox, go back to Account Settings, select your Exchange account, click Change, check Use Cached Exchange Mode, and set the slider to your preferred download period. Click Next, then Finish. Restart Outlook.

The shared mailbox now operates without a local .ost file. Error 8004010F will not occur because Outlook does not attempt to read a cached copy.

Step 3: Repair the Outlook Data File with Scanpst.exe

Scanpst.exe is the Microsoft Inbox Repair Tool. It scans and fixes corruption in Outlook data files. Use this method if you prefer to keep Cached Exchange Mode enabled for the shared mailbox.

1. Close Outlook completely
   Make sure Outlook is not running. Open Task Manager and verify no Outlook.exe process is active.
2. Find the shared mailbox .ost file location
   In Outlook, go to File > Account Settings > Account Settings. Select your Exchange account and click Change. Under Offline Settings, note the path shown next to Data File. This is the folder where your .ost files are stored. The shared mailbox .ost file is in the same folder. Its name usually matches the shared mailbox email address followed by .ost.
3. Locate Scanpst.exe
   The tool is installed with Outlook. For 64-bit Outlook, the path is: C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE. For 32-bit Outlook, the path is: C:\Program Files (x86)\Microsoft Office\root\Office16\SCANPST.EXE. If you use a different Office version, replace Office16 with Office15 for 2013 or Office14 for 2010.
4. Run Scanpst.exe on the shared mailbox .ost file
   Double-click Scanpst.exe. Click Browse, navigate to the .ost file for the shared mailbox, and select it. Click Start. The tool scans the file and reports any errors. Click Repair to fix them.
5. Restart Outlook
   Open Outlook and try to open the shared mailbox. The error should be resolved.

If Outlook Still Shows Error 8004010F After These Fixes

Outlook Keeps Using the Old Corrupted .ost File

If you removed and re-added the shared mailbox but the error persists, Outlook might still reference the old .ost file. Close Outlook. Open the folder where your .ost files are stored. Delete the .ost file that matches the shared mailbox email address. Restart Outlook and re-add the shared mailbox. Outlook creates a new .ost file automatically.

The Shared Mailbox Was Added by Auto-Mapping

If the shared mailbox appears automatically in your Outlook folder pane without manual addition, it is auto-mapped. Auto-mapped mailboxes are added by Exchange based on permissions. Removing the mailbox from Account Settings will not stop auto-mapping. You must ask your Exchange administrator to remove the auto-mapping attribute for your account in the Exchange admin center. After that, add the shared mailbox manually using the steps in this article.

Outlook Profile Is Corrupted

In rare cases, the entire Outlook profile is damaged. Create a new profile in Control Panel > Mail > Show Profiles > Add. Set the new profile as the default. Add your email account and the shared mailbox. This gives you a clean set of .ost files.

Manual Re-Add vs Auto-Mapping: Key Differences

Item	Manual Re-Add	Auto-Mapping
How the mailbox is added	User adds it through Account Settings > Advanced > Add	Exchange adds it automatically based on Full Access permission
Control over removal	User can remove it at any time	Only an Exchange admin can disable auto-mapping
Error 8004010F likelihood	Can occur if the .ost file becomes corrupt	Can occur if auto-mapping triggers a corrupt cache
Fix method	Remove and re-add the mailbox	Disable auto-mapping in Exchange admin center, then manually add the mailbox

Error 8004010F is a cache problem, not a server problem. You can fix it by removing the shared mailbox, disabling Cached Exchange Mode, or repairing the .ost file with Scanpst.exe. If the mailbox is auto-mapped, ask your administrator to disable auto-mapping and then add the mailbox manually. After the fix, the shared mailbox opens normally and syncs with the server without further errors.