Categorize your email
Categorizing your email and calendar can help you organize, and track
messages and events related to a project, task, or person. You can create new categories
and assign names and colors.
Below is the demonstration on how to categorize the emails.
Click on the settings (gear) and click on view all outlook settings
Under General you will see the categories options
Create a new category or edit the existing or leave as it is.
Go to the email, Right click and categorize the emails with the appropriate tag.
You can search the email according to the tag so that it will be easy for you to find the emails.