How do I remove Outlook mail from Spotlight?
You need to tell Spotlight not to search the Outlook Database on your local machine. 
Assuming you're using MS Office 2016 or later 
Here's how,


Open System Preferences > Spotlight
Click the Privacy Tab 
Locate your Outlook Database which can be found in the Library folder within you home folder. So /Users/userfolder/Library/Group Containers/UBF8T346G9.Office/
Drag the Outlook folder into the privacy tab you opened earlier within System Preferences.