Outlook Classic Search Not Working on Windows 11: Fix Indexing, OST Cache, and Windows Search (2026)

Start by testing the same search in Outlook on the web. Use a query you know should return results, such as a unique sender name or an exact subject line. If the web search returns results but Outlook Classic returns none, the problem is almost certainly local: indexing, cache, profile, or add-ins.

If web search also fails, pause here and investigate tenant/service-side factors before changing endpoints:

• Mailbox health
• Compliance holds affecting search
• Incident advisories

In Outlook Classic, click into the search box and look at the scope controls (for example: Current Mailbox, Current Folder, All Mailboxes). If you are searching a shared mailbox, an archive, or a specific folder, make sure your scope matches where the content actually is.

This step matters because Outlook can appear broken when it is simply searching "Current Folder" while the email you need sits in another mailbox or folder.

Outlook Classic search commonly depends on the Windows Search service. If it is stopped, disabled, or stuck, Outlook's indexed search will degrade or fail.

Open Services (services.msc) and confirm Windows Search is running. If it is running but Outlook search is still empty, restart the service once. After restart, give the system a few minutes to settle; immediate retesting can be misleading because indexing may need to resume.

Open Control Panel → Indexing Options. You are looking for a very specific item: Microsoft Outlook must be listed among the indexed locations. If Outlook is not selected, Outlook may show partial results or none at all even if Windows Search is functioning.

If Outlook is missing from indexed locations, enable it, apply changes, and then continue to the next step (rebuild) only if search remains broken.

This is the most effective repair step for "no results" and "incomplete results" cases when Outlook is already included in indexed locations.

Steps to rebuild:

1. Go to Control Panel → Indexing Options
2. Click Advanced
3. Click Rebuild

This deletes and recreates the Windows Search index. After you start the rebuild, leave the device plugged in and online, and avoid rebooting repeatedly. Index rebuild is not instantaneous; Outlook search quality improves progressively as indexing completes.

Return to Indexing Options and read the status line. If it shows items remaining, the index is still building. During this period, Outlook searches can appear inconsistent: recent mail might not be searchable yet, and body searches may fail until content is indexed.

When indexing reports completion, test Outlook search using a query that should return many items. At that point, if results are still missing, move to the offline mail and OST steps next.

If Outlook search cannot find older messages but web search can, the root cause is often Cached Exchange Mode configuration. Outlook can only index what is available locally in the OST. If you only keep 3 months offline, you should expect search gaps beyond that window.

To increase offline sync window:

1. Open Outlook → File → Account Settings → Account Settings
2. Select your account and click Change
3. Increase the Mail to keep offline slider

Then allow Outlook time to download older items. After download progresses, indexing also needs time to catch up.

If Windows indexing is complete and Outlook is indexed, but search still returns incomplete results, treat the OST as suspect. This is particularly effective when users report "search worked yesterday, then suddenly stopped," or when only some folders are searchable.

To rebuild the OST:

1. Close Outlook completely
2. Locate the OST file path (Control Panel → Mail → Data Files, or Account Settings)
3. Rename the OST file (for example, add .old)
4. Reopen Outlook and let it rebuild the mailbox cache

Once the OST rebuild starts, give it time, then allow indexing time again.

Start Outlook in Safe Mode to disable COM add-ins temporarily. If search works in Safe Mode but not in normal mode, an add-in is likely interfering. Disable non-essential add-ins and re-test.

This matters in enterprise because archive connectors, CRM plugins, and security add-ins can hook Outlook events in ways that degrade search or block content indexing.

If search is still broken after indexing and OST repair, perform an Office repair. Use Quick Repair first because it is faster and less disruptive. If it fails, use Online Repair as the final software-layer remediation.

After the repair, reboot once and test search again. If search starts working, avoid additional changes and allow indexing to stabilize.

Create a new Outlook profile:

1. Open Control Panel → Mail → Show Profiles
2. Click Add to create a new profile
3. Add the same Microsoft 365 account
4. Test search in the new profile

This step is a clean way to rule out profile-level corruption, and it often resolves "only this one user" cases without requiring OS-level work. If the new profile fixes search, you can migrate the user to it permanently and archive the old profile for rollback if needed.

If the issue started immediately after a Windows 11 or Office update, update-driven behavior should be part of your root cause analysis. The right pattern is: patch forward when a fix is available, and only rebuild once after the system is on a stable build. If you rebuild the index repeatedly while the underlying regression remains, you keep paying the indexing cost without resolving the trigger.

In managed environments, validate in a pilot ring first, then roll out broadly once you confirm search stability. Document the change as an update regression with endpoint evidence: OS build, Office build, indexing status, and whether web search was unaffected.