First, Technology Services recommends using Outlook Web to do detailed searches in your mailbox.
But if you notice that your searches are stopping too soon or the results just seem incorrect, make sure this setting is disabled:

1)  Login to your account using Outlook Web at https://mail.office365.com

2)  Click on Settings in the upper right   
3)  Navigate to the MAIL section and MESSAGE ORGANIZATION and make sure it's set to DO NOT GROUP MESSAGES:

 


4)  Try your search again, you should see more results.

If you still are having problems, just contact the Helpdesk at [email protected] so we can investigate it further.