Header analyzer tools will parse a message for you in seconds. What they won’t do is teach you what you’re looking at — which is exactly the gap Chapter 11 fills, organized by symptom, not by field.
Email delayed? Compare Received timestamps hop by hop. Email bounced? Decode the SMTP response text embedded in the notification. Landed in spam despite looking legitimate? Cross-reference Authentication-Results against the spam-scoring headers from Chapter 10. Looks spoofed? Compare From, Return-Path, and the origin of the first Received header against each other.
Each path ends at a specific header field that confirms the diagnosis — not a vague “check your headers” suggestion, but the exact field name and what value would confirm or rule out the theory.