When you’re having trouble with searches in Microsoft Outlook, there’s a possibility that a corrupted search index is to blame. Rebuilding it may fix the problem.
Sometimes when migrating emails, rebuilding PST files, and enabling additional mailboxes, the Outlook search index can fail to update or even become corrupted. This isn’t something that happens too often, but if you are frequently moving emails between different computers, then the odds drastically go up. Most problems with the search index can be fixed by deleting and rebuilding it, so let’s do that.
Rebuild Outlook Search Index
In Outlook 2013, click the File ribbon and then select Options.
Once the Outlook Options window appears, click the Search tab from the left column.
At the right side of the right pane, click the Indexing Options button.
Another smaller window should appear titled Indexing Options. Click the Advanced button here. Note: This may require administrator privileges.
Next on the default Index Settings tab click the Rebuild button.
Outlook will prompt with a warning that rebuilding the index may take a long time to complete. Also, while the index is being rebuilt searches probably won’t work. Click OK to begin the rebuild.
There isn’t a set way to determine the amount of time it will take to build the index. It varies depending on the number of emails, file size, and processing power of the computer.
Back on the Indexing Options window, the status will update at the top. It should start out by showing the items currently indexed and the status of the index rate below it. If you have other applications running in the background then it will display a message saying “indexing speed is reduced due to user activity.”
Once Outlook finishes building the index it will say that Indexing is complete in the status window.