How To Fix Outlook Search Returns Incomplete Results.

When you get incomplete results using Outlook search, follow these steps in the order provided:

Include Delete Folder

If the missing search results are in the Deleted items folder, you can add this folder to your search results:

Click File > Options, and then select Search
Select the Include messages from the Deleted Items folder in each data file when searching in All Items checkbox, and click OK

Increase the sync slider to download email for the past

you can increase the time in your email account’s offline settings so that more or all your emails are cached locally for indexing. To do this:

Drag the Download email for the past: slider to the desired amount of time or to the far right to All.

5.Click Next, and then Done. Closeout the window and restart Outlook.
Allow the search to show all results

By default, Outlook will display 250 search results. You can increase this to show all results but the search will be slower.

To do this:
1.Open Outlook.
2.Click File > Options, and then select Search.

3.Clear the Improve search speed by limiting the number of results shown checkbox, and click OK.

4.Restart Outlook.