Quick answer: Close Outlook, open Indexing Options, click Advanced, then Rebuild under Troubleshooting. Wait a few hours, and search usually works again.
If you're here, you've probably just gone through a Windows update—maybe a feature update like 22H2 or a monthly cumulative patch—and suddenly Outlook search is either spinning forever or returning zero results for emails you know are sitting right there. I've seen this at a dozen client sites. Last month, a real estate office called me because their agent couldn't find a signed contract from two weeks ago. Search pulled up nothing, but the email was in the folder. Classic index corruption.
What happens is the Windows Search service, which handles Outlook's search, builds an index of your mailbox content. When Windows updates, it can reset or invalidate parts of that index—sometimes because the service gets interrupted mid-write, sometimes because the update changes how the indexer stores data. The result is an index that points to deleted or changed items, so search fails even though your emails are fine.
Here's the fix that works in most cases. I've done this on Windows 10 and 11, Outlook 2016 through Microsoft 365.
Step 1: Verify Outlook search is actually broken
Before you nuke the index, run a simple test. In Outlook, go to the Search box at the top, type something you know exists, and check the status bar at the bottom—it might say "Search results may be incomplete." If you see that, or if it hangs, proceed. If it says "Searching" but never finishes after a few minutes, also proceed.
Step 2: Close Outlook completely
You'd think this is obvious, but I've had people try to rebuild while Outlook is running, and it doesn't work right. Make sure Outlook is fully closed, including the notification area icon. Right-click the Outlook icon in the system tray and choose Exit.
Step 3: Open Indexing Options
Hit the Windows key, type Indexing Options, and hit Enter. That opens the control panel applet. You'll see a list of indexed locations, and Outlook should be in there. If it's not, that's a problem—we'll cover that later.
Step 4: Advanced rebuild
Click the Advanced button at the bottom. In the new window, under "Troubleshooting," click Rebuild. It'll warn you that indexing might take a while. Accept.
Now close that window and wait. That's the hard part. Depending on your mailbox size and PC speed, indexing can take anywhere from 30 minutes to a few hours. I've seen a 50GB mailbox take most of a day on an older i5. Don't rush it. You can keep using your computer, but if you open Outlook before indexing is done, search will be partial—and it might seem broken again, so resist the urge.
You can monitor progress by opening Indexing Options again—it shows how many items are remaining. Also, check the Windows Search service is running. Open Services (Win+R, type services.msc), find Windows Search, and make sure it's not stopped and set to Automatic.
If the rebuild doesn't fix it
Sometimes the index rebuild itself fails or Outlook still can't find anything. That happened at a law firm I worked with—rebuild completed but search was still dead. Here's what to try next.
Delete the index files manually
Close Outlook and all Office apps. Open Services, stop Windows Search. Then delete the entire contents of this folder:
%ProgramData%\Microsoft\Search\Data\Applications\WindowsDon't delete the folder itself, just what's inside. Then restart Windows Search from the Services console. Windows will rebuild from scratch. This is more thorough than the Rebuild button—it wipes any corrupt database files that might not reset properly.
Check your Outlook profile
If search is still broken, the issue might be the mailbox itself—not the index. Create a new Outlook profile (Mail control panel → Show Profiles → Add) and set it as default. Then start Outlook and see if search works. If it does, your old profile's data files (PST/OST) might be corrupted. Run scanpst.exe on the old file if that's the case.
Run the built-in repair
Microsoft Office has a repair tool. Go to Settings → Apps → Installed apps, find Microsoft 365 or Office, click Modify, and choose Quick Repair. If that doesn't help, do Online Repair—it takes longer but replaces all Office files. I usually go straight to Online Repair because Quick Repair doesn't touch search components.
Prevention for next time
You can't stop Windows Update from messing with your index, but you can make recovery faster. Set aside time after any big update—like the twice-a-year feature updates—to run the rebuild proactively. If you manage a fleet, schedule this a day after updates roll out. Also, keep your mailboxes tidy: the more items, the longer the index takes. Archive old mail instead of letting it pile up.
One more thing: if you're using Outlook in cached mode (which is the default), make sure you have enough free disk space. Indexing needs room to breathe. I've seen search fail just because the C: drive was 98% full—the indexer couldn't write new entries. Free up at least 10GB and it made a world of difference.
That's the whole playbook. Rebuild the index first, because nine times out of ten, that's the fix. If it's not, then you're dealing with a profile or file issue, and you handle that separately. Search is one of those things you don't appreciate until it's gone—but now you know how to get it back.