Email display-name branding mismatched against support-subdomain header-From domain

Detects phishing attempts where the sender's display name implies a sensitive role (e.g., Accounts Payable, Helpdesk, Vendor) while the authenticated header-From domain utilizes a 'support' subdomain. The rule triggers when the organizational root domain extracted from the email sender address does not match the branding present in the sender display name, indicating potential brand impersonation or business email compromise.