On demand disable forwarding? OWA and Outlook?

This is nothing new, the only new part about it is that it got included as part of the Secure Score recommendations/actions: https://blogs.technet.microsoft.com/office365security/mitigating-client-external-forwarding-rules-with-secure-score/

Here's the actual rule syntax: IF The Sender is located ‘Inside the organization’ AND IF The Recipient is located ‘Outside the organization’ AND IF The message type is ‘Auto-Forward’ THEN Reject the message with the explanation ‘External Email Forwarding via Client Rules is not permitted’