Description: Use the function to report/mark suspicious email with malicious intent or classify an email as junk or spam. 

Desktop Outlook Application

Step 1: Select an Email 

Step 2: At the Top (Far Right) Navigational Options > Report Message

Step 3: Select one of the three options and note that Junk is also use to report Spam.

Office 365 Email (Web Interface)

Step 1: Select an Email and have it open in the reader pane.

Step 2: Select Junk from the navigational options