Outlook search is slow or not finding emails
What causes Outlook search to miss mail or crawl, how to rebuild the Windows index, and what to do when rebuilding does not help.
Outlook search leans on the Windows Search index. When that index is incomplete or damaged, Outlook does not tell you. It returns fewer results and looks like it worked.
Check whether Outlook has finished indexing
In Outlook, click the search box, then Search Tools, then Indexing Status. If it reports items remaining, search results are incomplete until that number reaches zero. On a large mailbox after a fresh install this can take hours.
Confirm Outlook is actually being indexed
Open Indexing Options from the Start menu, click Modify, and check that Microsoft Outlook is ticked. It gets switched off by profile changes and by some managed-computer policies.
Rebuild the index
In Indexing Options, click Advanced, then Rebuild. Expect several hours on a large mailbox, and expect search to be worse until it finishes. Rebuild once. Rebuilding repeatedly is the most common way people lose a day.
When the mailbox is not on your computer
If your account is set to keep only a few months of mail offline, Outlook can only search what it has. Everything older is searched by the server, which is slower and behaves differently. In Account Settings, Change, move the Mail to keep offline slider to All. That makes the local file larger and takes time to download, but it is why older mail seems to vanish from search.
Why rebuilding sometimes changes nothing
Windows Search is shared by every program on the computer and is not tuned for a 200,000 message mailbox. On very large mailboxes it falls behind permanently: it finishes, then falls behind again as mail arrives. There is no setting that fixes this, which is the honest answer most pages on this subject will not give you.
At that point the options are to accept it, to archive aggressively so the mailbox is smaller, or to use a search tool that keeps its own index of your mail instead of relying on Windows Search.
KAM-Q builds a private search index of your mailbox on your own computer, so results appear as you type. It works with classic Outlook on Windows and Mac, and with Apple Mail. Your mail never leaves your machine. Try it free for 7 days.