Implementing SelectionChange event without taskpane

I am getting requrement from client that is add catetory in mailitem based on content of mailitem. I am passing email content to third party system and analyze content and set categories based on Content. 

Without task pane pin, I unable to trigger selectionChange event in Outlook Item.

Solution:

We can add SelectionChange Event in LaunchEvent supporting category. It is also called Event based activation 

Detail https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/autolaunch#supported-events