A security engineer discovers that some legacy systems are still in use or were not...

The presence of an unauthorized server (29mail.mycrosoft.info) sending emails on behalf of the company indicates a potential spoofing or phishing attempt. To mitigate this:

Remove the unnecessary servers from the SPF record (Option C):The Sender Policy Framework (SPF) specifies which mail servers are authorized to send emails on behalf of a domain. Removing unauthorized or unnecessary servers from the SPF record helps prevent spoofed emails from passing SPF checks.

Change the SPF record to enforce the hard fail parameter (Option D):Setting the SPF policy to a hard fail (-all) ensures that emails from unauthorized servers are rejected, enhancing email security.

Implementing these changes strengthens the domain's email authentication mechanisms, reducing the risk of successful phishing or spoofing attacks.