https://www.bleepingcomputer.com/news/security/office-365-to-stop-data-theft-by-disabling-external-forwarding/

Microsoft is planning to put a stop to enterprise data theft via email forwarding by disabling Office 365's email forwarding to external recipients by default.

The company also wants to add improved external email forwarding controls which will allow Office 365 admins to enable the feature only to select employees in their organizations.