The cybersecurity response team at a global enterprise receives an alert from an employee regarding...

Comprehensive and Detailed Explanation (ECIH-aligned):

The ECIH Email Security Incident Handling module emphasizes email header analysis as a primary method for identifying spoofed or malicious emails. One of the most critical header elements is the originating IP address, which reveals where the email actually came from.

Option D is correct because tracing the originating IP and validating it through WHOIS provided definitive evidence that the email did not originate from a legitimate organizational source. This technique allows responders to distinguish between legitimate executive communications and impersonation attempts.

Option A is reactive and unreliable. Option B provides detection context but not attribution. Option C validates domain authentication but does not always reveal spoofing when credentials are compromised.

ECIH highlights that IP tracing combined with WHOIS analysis is a powerful verification method during executive impersonation investigations, making Option D correct.