How to prevent users from enabling automatic forwarding outside the organization 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 Automatic forwarding section and select Off – Forwarding is disabled from the drop-down box.

Step 6: Click on Save.