This detection rule identifies potential phishing attempts that exploit Cisco's secure email service (res.cisco.com). It focuses on messages related to financial topics or requests for invoices that display inconsistencies, such as mismatched reply-to domains and the presence of undisclosed recipients. Specifically, it checks if the incoming messages are sent from the Cisco domain, and if they contain financial content through analysis of the message body or subject line. The rule raises the alarm for potential Business Email Compromise (BEC) or fraud scenarios, which are characterized by impersonation, social engineering tactics, and attempts to evade detection. Techniques like content analysis, header analysis, natural language processing, and sender validation are employed to ensure effective detection. This is crucial for organizations relying on Cisco's email systems to prevent malicious exploitation.