Forum Discussion
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’
To be specific, what Vasil has highlighted is an Exchange transport rule that will check for messages autoforwarded by users and block them. The advantage of this approach is that it is guaranteed to work because all email must flow through the transport system and be checked against the tenant's rules. However, introducing such a rule without prior advice and consultation with users might provoke a negative reaction from people, so perhaps user education is a better first step.