How to Rebuild the Outlook Search Index (Windows Search)

Outlook search stops returning results, starts missing emails from last month, or silently excludes an entire folder — and the advice you find almost everywhere is to rebuild the search index. That advice is right, but only for one version of Outlook. Run the procedure on the wrong one and you will spend an afternoon clicking through dialogs that will not fix anything, because the index those dialogs control is not what your Outlook is using.

This guide covers how to rebuild the Outlook search index on Windows, how to tell when a rebuild is still running, how long it realistically takes on a large mailbox, and what to do when the rebuild does not fix the problem. It also covers the platform difference that makes all of this irrelevant on new Outlook and the web — because the single biggest source of wasted time on this topic is rebuilding a local index for a version of Outlook that has no local index.

Before you start: classic Outlook or new Outlook?#

The most important thing to check before opening Indexing Options is which version of Outlook you are running, because the answer determines whether a local index rebuild is relevant at all.

Classic Outlook — the traditional desktop application distributed through Microsoft 365 Apps for Enterprise, Microsoft 365 Personal and Family, and Office perpetual installs — maintains a local search index managed by Windows Search. When search breaks in classic Outlook on Windows, rebuilding that index is often the right fix. The steps below apply to this version.

New Outlook for Windows is a web-architected client, rebuilt on the same codebase as Outlook on the web. It does not maintain a local index at all. Search in new Outlook runs on Microsoft's servers, the same way it does in a browser tab. There is no Indexing Options entry for new Outlook, no local cache to rebuild, and no local rebuild procedure that will help. If search is broken in new Outlook, the cause is almost always a network or account sync issue, not a local index problem.

You can tell the two apart quickly: in classic Outlook, the title bar shows the account name and version, and File > Office Account shows your product. In new Outlook for Windows, the interface is noticeably flatter and matches outlook.com, and there is no backstage File menu, only a Settings gear. Microsoft began offering new Outlook as an opt-in in early 2025 and made it the default for new SMB installs. Enterprise opt-out does not begin until 1 March 2027, per Microsoft message centre post MC949965, and classic installs are supported at least until 2029.

How to rebuild the Outlook search index on Windows#

The steps below apply to classic Outlook on Windows with Windows Search enabled. Outlook must stay open and connected throughout — closing it pauses the rebuild mid-way.

1. 1

   Open Outlook Options

   In classic Outlook, click File in the top-left corner to open the backstage view, then click Options near the bottom of the left panel. The Outlook Options dialog opens.

2. 2

   Navigate to Search settings

   In the left panel of Outlook Options, click Search. The right panel shows search settings, including sources and the Indexing Options button.

3. 3

   Open Indexing Options

   Click the Indexing Options button. This opens the Windows Search Indexing Options dialog, which lists all locations currently being indexed on your machine.

4. 4

   Confirm Outlook is an indexed location

   Check that Microsoft Outlook appears in the included locations list. If it is missing, click Modify, expand the Microsoft Outlook entry under the email section, check the box, and click OK. Outlook must be an indexed location before a rebuild will help.

5. 5

   Open Advanced Options

   Click the Advanced button. You may need local administrator rights. This opens the Advanced Options dialog with index settings and troubleshooting controls.

6. 6

   Rebuild the index

   Under the Index Settings tab, click Rebuild in the Troubleshooting section. Confirm when prompted. Windows Search will delete the current index and start building a fresh one from scratch.

7. 7

   Leave Outlook open and monitor progress

   The Indexing Options dialog shows the remaining item count as it processes. Closing Outlook pauses the rebuild. Leave both Outlook and the dialog open until the count reaches zero or the status line reads Indexing complete.

Platform differences: which Outlook versions use a local index?#

The table below shows how search works across the main Outlook platforms and whether a local index rebuild applies to each.

How long does Outlook indexing take, and how do you check the status?#

Rebuild time depends on mailbox size, hardware speed, and whether you are using Cached Exchange Mode. On a modern SSD with a few thousand emails, a rebuild typically finishes in under an hour. On a large mailbox — tens of thousands of emails, a multi-gigabyte OST file, or a machine with a slower drive — a full rebuild can take several hours. Search results will be incomplete for the duration.

You can check progress in the Indexing Options dialog: the status line beneath the location list shows the remaining item count and either a progress message or Indexing complete. Outlook also shows a message in the status bar at the bottom of the main window while indexing is still running.

A few things slow the rebuild down or stop it entirely. Closing Outlook pauses indexing. A laptop going to sleep pauses it. A large OST file on a mechanical drive extends it significantly. If you need search working immediately and the rebuild is still in progress, you can switch to server-side search: go to the Search tab in the Outlook ribbon, click Search Tools, then Search Options, and change the search scope from Local to Server. This bypasses the local index and queries the mailbox on the Microsoft server directly, at the cost of slightly slower response times.

What to do when rebuilding the index does not fix Outlook search#

A successful rebuild resolves most Outlook search problems on Windows, but not all. If search is still broken after the index count reaches zero, work through the following causes in order.

If none of the above resolves the problem and you are running classic Outlook against a Microsoft 365 mailbox, the issue may be on the server side rather than local. Switch the search scope to Server (Search tab > Search Tools > Search Options > Search in: Server) and see if server-side search returns the missing emails. If it does, the local index is the problem and needs attention. If server-side search also fails, contact Microsoft support — the issue is upstream of your machine.

A faster way: search that does not depend on a local index#

Rebuilding the Windows Search index is a manual fix for a recurring problem. Classic Outlook's local index breaks after Windows updates, mailbox migrations, and large OST files — and each rebuild means hours of incomplete search while Windows works through the backlog. The underlying fragility is the local index itself: a layer sitting between you and your mail that needs periodic maintenance.

AI Emaily's smart search queries your mailbox directly without relying on a local Windows index. It uses semantic search, so you can describe what you are looking for rather than recalling the exact subject line — 'the contract from Maria in June' returns the right thread even if those words do not appear together anywhere in it. There is no index to rebuild, no stale cache to clear, and no period of incomplete results. Search works the same way across every connected account — Outlook, Gmail, and others — from a single interface. We build AI Emaily. You can explore it at aiemaily.com and review the 7-day trial on the Pro and Autopilot plans at aiemaily.com/pricing.