Forged Healthcare Sender Phishing: DKIM Fail + Invoice Lure + HolaBrief/LoopedIn Redirect

This rule monitors inbound emails that exhibit signs of phishing, specifically looking for failures in email authentication protocols (DKIM, DMARC), the use of specific invoice-themed subject lines, and the inclusion of redirection links pointing to known third-party collaboration platforms (HolaBrief, LoopedIn). It also identifies cases where the sender's envelope domain differs from the header's 'From' domain, which is a common indicator of email spoofing used in identity-based attacks.