This detection rule identifies potential executive impersonation attempts that leverage email addresses from free email providers. Specifically, it looks for patterns in the sender's email address, where the local part of the email contains the terms 'chair' or 'ceo' followed by digits, indicating a likely attempt to masquerade as high-level executives. The inclusion of numeric values in conjunction with these terms is a common tactic used by attackers to create plausible-sounding email addresses that may deceive recipients into believing they are communicating with legitimate executives. By focusing on these characteristics, the rule aims to prevent Business Email Compromise (BEC) and fraud instances that exploit social engineering methods.