When you are getting issue in Outlook Search Index especially while searching Outlook Emails and other items, then it might be possible that your Outlook search index is corrupt. So, to sort out this issue, you can try to rebuild Outlook Search Index.
To rebuild Indexing Options in Outlook, you have various methods to reach:
Here, I am going to show you steps in Microsoft Outlook 2010:
It should be remembering that at the time of rebuild index process, if you search anything in the Microsoft Outlook; it probably will not work or will not pull up anything. And also, the time duration of Rebuild Indexing process depends upon the PST file size, number of emails, etc. So, you have to wait until the completion of process.
If you want to see the status of rebuild indexing process, then see on the top of "Indexing Options" window as I showed in given below screenshot. If there is any application running in the background, then a text will be showing to you i.e. Indexing speed is reduced due to user activity.
After the competition of rebuild index process, press "CTRL" + "E" button (combine) while Microsoft Outlook is active window and checked the searching is working perfectly in Outlook.