This rule is designed to detect potential callback phishing attacks that exploit distribution lists. It looks for emails from unknown domains that leverage Sender Rewrite Scheme (SRS), indicating relay through a distribution list, aimed at a recipient with no prior interaction with the organization. The detection is contingent on several conditions: the sender domain must not be from a free email provider, the recipient email must also be from outside the organization's domains, and the structure of the email headers must suggest automatic forwarding or relaying. The rule checks return paths and SPF records to confirm the use of SRS, ensuring the return path does not match domain patterns associated with the organization. Additionally, it validates against known dangers by ensuring no response addresses or reply-to headers correlate with the organization, which helps mitigate spoofing attempts related to phishing.