Exchange mail - only default mail folders will download

Question

Hi, I just setup a new customer with office 365 exchange email.

I downloaded their old mail to a pst file,

then I uploaded the email to the new exchange account.

I can see all the email online in a browser.

When I enter in the email address in outlook 365 app on the desktop, all the folders get downloaded, but the user created folders have no mail in them, just the default mail folders have mail.

Answer 1

Hi @Adrien - D.C. Computers Inc, 

Thank you for clearly describing your migration steps and for confirming the messages are visible in the browser. 

From your description, you can see all migrated messages in Outlook on the web, however in Outlook for Windows the default folders download with mail while the user created folders appear empty. 

This usually happens when Outlook is using Cached Exchange Mode and is currently displaying only what has been synchronized into the local offline cache rather than the full mailbox on the server. In addition, if the cached window is limited, folders that mainly contain older items can look empty until Outlook is set to keep more mail offline and completes a full sync. In some cases, the messages are present but a folder view filter hides them from the current view. 

Below are some workable options that might be the most appropriate for your current situation:  

1/ Expand the offline cache window so Outlook downloads older content 

• Open Outlook, select File, then select Account Settings, then select Account Settings again. 
• Select the Microsoft 365 or Exchange account, choose Change, and then set Mail to keep offline to All. 
• Close Outlook and reopen it so the mailbox can resynchronize, then allow time for the folders to repopulate. 
• Reference: Only a subset of your Exchange mailbox items is synchronized in Outlook

2/ Remove any folder view filters that may be hiding items 

• Select one of the user created folders that shows no messages. 
• Select the View tab, open View Settings, and then select Filter. 
• Clear any filtering conditions such as date received, read or unread, sender, or keywords, and then apply the change to confirm the messages become visible. 
• Reference: Items disappear or are not visible in an Outlook folder

3/ Rebuild the local cache so Outlook re downloads the mailbox content cleanly 

• In Outlook, go to File, then Account Settings, then Account Settings, select the account, and choose Change. 
• Under Offline Settings, clear Use Cached Exchange Mode, close Outlook, and then reopen it to force an online refresh of the mailbox view. 
• Re-enable Use Cached Exchange Mode, restart Outlook again, and then let synchronization complete so the OST cache is rebuilt. 
• Reference: Turn on Cached Exchange Mode 

4/ Contact IT administrator:    

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.         

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn   

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.       

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.         

Thank you for your patience and your understanding. I look forward to continuing the conversation.  

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Answer 2

In this scenario the mailbox data is present in Exchange Online (visible in the browser), but Outlook on Windows is not downloading items in user‑created folders. This is typically caused by how Cached Exchange Mode is configured for shared/non‑default folders.

Use these steps to resolve and verify:

1. Check Cached Exchange Mode settings
   1. In Outlook, go to File → Account Settings → Account Settings….
   2. Select the Exchange account → Change.
   3. Ensure Use Cached Exchange Mode is enabled.
   4. If there is a Mail to keep offline slider, move it to All.
   5. Restart Outlook and give it time to fully synchronize.
2. Verify that all folders are selected for synchronization
   1. In Outlook, right‑click the top of the mailbox (the email address) → Data File Properties (or Properties).
   2. Click Folder Size….
   3. Compare the Server Data and Local Data tabs. If items exist on the server but not locally for user folders, the cache is incomplete.
3. Rebuild the local cache (OST)
   1. Close Outlook.
   2. In Control Panel → Mail → Data Files, select the Exchange account and note the OST file path.
   3. Exit Outlook completely (ensure no Outlook.exe in Task Manager).
   4. Rename the OST file (for example, add .old).
   5. Start Outlook; it will create a new OST and re‑download all folders and items. Check the user‑created folders again.
4. Check for rules or system folders issues
   • If rules are moving items into unexpected or system folders (such as Files, Files1, etc.), those items may not appear in normal user folders. In some Exchange Online tenants, Files and similar system folders are hidden and not user‑accessible, and items placed there must be moved out with tools like MFCMAPI.
   • If migration logs or errors mention conflicts with a Files folder, inspect that folder with MFCMAPI, delete or move any items out of it, and then resync or re‑run the migration batch.
5. If only default folders show items and all steps above fail
   • Remove and recreate the Outlook profile:
     1. Close Outlook.
     2. Control Panel → Mail → Show Profiles….
     3. Add a new profile, configure the same Exchange Online account, and set the new profile as default.
     4. Start Outlook with the new profile and allow full sync.

If, after recreating the profile and OST, the items still only appear in Outlook on the web and not in the desktop client, collect any migration error details (especially folder conflict errors like with Files) and address those before trying another sync or migration batch.

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References:

• Exchange Online hides previously displayed Files and folders
• Manage download settings for shared mail folders in Cached Exchange mode in Outlook
• AggregateMailboxFolderConflictPermanentException Exchange Hybrid Migration - Microsoft Q&A
• "Error: default folders cannot be moved or deleted" error message when you migrate on-premises mailboxes to Office 365