How to receive an alert if a user is sending suspicious emails in Office 365?

Step 1: Sign into Office 365 admin portal via https://portal.office.com

Step 2: Click on Admin from the left pane and navigate to Security center.

Step 3; Now navigate to Threat Management > Policy > Anti-spam settings.

Step 4: Expand Outbound spam filter policy ‎(always ON)‎ and click on Edit policy.

Step 5: Expand Notifications section and check the Notify specific people if a sender is blocked due to sending outbound spam checkbox.

Step 6: Click on Add people button and then enter the users and click on the + button.

Step 7: Click on Save.