Outlook Search Does Not Include Online Archive: Fix

When you search in Outlook, results from your Online Archive mailbox are missing. This happens even when you know the email exists in the archive folder. The root cause is that Outlook search defaults to the primary mailbox index and does not automatically include the Online Archive index. This article explains why this separation occurs and provides a direct fix to make search results include both mailboxes.

The Online Archive is a separate mailbox in Exchange Online or Microsoft 365. Outlook treats it as a distinct data file with its own search index. By default, the global search scope only covers the primary mailbox. You must manually tell Outlook to search the archive as well.

This article covers the exact steps to change the search scope, rebuild the archive index if needed, and verify that the fix works. It also explains related search failures and how to avoid them.

Why Outlook Search Excludes the Online Archive by Default

The Online Archive is a secondary mailbox that stores older email to reduce the size of your primary mailbox. When you perform a search in Outlook, the application communicates with the Windows Search service to query the index. By default, Windows Search only indexes the primary Outlook data file and the local OST file for the primary mailbox. The Online Archive mailbox has its own OST file and its own index entry. Because the default search scope is limited to the primary mailbox, the archive is not queried.

This behavior is by design in Exchange Online and Microsoft 365. The archive is a separate mailbox object with a separate folder hierarchy. Outlook does not merge the two indexes. The fix involves either temporarily expanding the search scope during each search or permanently adding the archive to the Windows Search index.

How the Search Index Works with Online Archive

Windows Search maintains an index of all Outlook items in the local OST files. Each mailbox, including the archive, has its own OST file located in %localappdata%\Microsoft\Outlook. The indexer treats each OST file as a separate data source. If the archive OST file is not included in the index locations list, search will skip it entirely. This is the most common reason why searching from the primary mailbox returns zero results from the archive.

Steps to Include the Online Archive in Outlook Search

There are two methods to fix this problem. The first method changes the search scope for an individual search session. The second method permanently adds the archive to the Windows Search index. Use the second method if you search the archive regularly.

Method 1: Set Search Scope to All Mailboxes

1. Open the Search tab
   Click inside the search box at the top of the Outlook window or press Ctrl+E. The Search tab appears on the ribbon.
2. Click Search Tools
   In the Search tab, locate the Search Tools group on the right side of the ribbon. Click Search Tools.
3. Select Search Scope
   From the dropdown menu, point to Search Scope and then select All Mailboxes. This tells Outlook to search the primary mailbox and the Online Archive.
4. Type your search query
   Enter your search term in the search box. Results from both mailboxes now appear in the same list, with the mailbox name shown next to each result.

This method works for the current search only. When you clear the search box and start a new search, the scope resets to the primary mailbox. Repeat these steps each time you need to search the archive.

Method 2: Add Online Archive to the Windows Search Index

1. Open Outlook Options
   Click File > Options > Search.
2. Open Indexing Options
   In the Search section, click Indexing Options. A separate window opens showing the current index status.
3. Click Modify
   In the Indexing Options window, click the Modify button. A list of indexed locations appears.
4. Expand Microsoft Outlook
   Scroll down and expand Microsoft Outlook. You will see the primary mailbox listed. If the Online Archive is not listed, close the Indexing Options window and proceed to the next step to locate the archive OST file manually.
5. Locate the archive OST file
   Press Windows+R, type %localappdata%\Microsoft\Outlook, and press Enter. Look for a file named archive.ost or a file that contains the word archive in the name. Note the full path.
6. Add the archive OST folder to the index
   Return to Indexing Options and click Modify. Click Show all locations at the bottom. Navigate to the folder you found in the previous step and check the box next to it. Click OK.
7. Rebuild the index
   In Indexing Options, click Advanced. Under Troubleshooting, click Rebuild. Confirm the rebuild. This forces Windows Search to reindex all items, including the archive OST file. The rebuild may take several hours depending on the size of your mailboxes.

After the rebuild completes, perform a test search from the primary mailbox. Results from the Online Archive should now appear automatically without changing the search scope.

If Outlook Search Still Does Not Include the Online Archive

Two additional problems can prevent archive search results even after following the methods above. Below are the specific fixes for each scenario.

Search Returns Only Results from the Primary Mailbox

If you set the scope to All Mailboxes but only see primary mailbox results, the archive mailbox may not be fully synchronized. Go to File > Account Settings > Account Settings. Select your Exchange account and click Change. Under Offline Settings, ensure Download shared folders is checked. This includes the archive in the sync. Click Next and restart Outlook.

Archive OST File Is Missing or Corrupt

If the archive OST file is missing, Outlook cannot index it. Open Outlook and navigate to the Online Archive folder. Right-click the archive root folder and select Data File Properties. Click Advanced and note the path of the OST file. If the file does not exist at that path, close Outlook, delete the archive OST file from the %localappdata%\Microsoft\Outlook folder, and restart Outlook. Outlook recreates the OST file and synchronizes the archive again. Then repeat Method 2 to add the file to the index.

Search Scope Options: Primary Mailbox vs All Mailboxes

Item	Primary Mailbox Only	All Mailboxes
Default search scope	Yes	No
Includes Online Archive	No	Yes
Includes shared mailboxes	No	Yes, if added to profile
Index rebuild required	No	Only if archive OST is not indexed
Persists between searches	Yes	No, must be set each session
Keyboard shortcut to set	None needed	Ctrl+E then Alt+H, S, S

Use the All Mailboxes scope for ad-hoc searches that require archive results. For daily use, add the archive OST file to the Windows Search index using Method 2 so that the default scope includes the archive automatically.

You can now force Outlook search to include the Online Archive mailbox by either changing the search scope to All Mailboxes or by adding the archive OST file to the Windows Search index. After applying Method 2, the archive is permanently indexed and searchable from the primary mailbox without extra steps. To verify the fix, press Ctrl+E and type a term you know exists in the archive. If results appear, the fix is complete. As an advanced tip, you can create a quick step in Outlook that automatically sets the search scope to All Mailboxes and runs a specified search query, saving you from manually selecting the scope each time.