Agent skill

analyzing-phishing-email-headers

Email headers contain critical metadata that reveals the true origin, routing path, and authentication status of emails. Analyzing these headers is a foundational skill for identifying phishing attemp

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npx add-skill https://github.com/autohandai/community-skills/tree/main/analyzing-phishing-email-headers

SKILL.md

Analyzing Phishing Email Headers

Overview

Email headers contain critical metadata that reveals the true origin, routing path, and authentication status of emails. Analyzing these headers is a foundational skill for identifying phishing attempts, verifying sender authenticity, and gathering threat intelligence. This skill covers systematic extraction and interpretation of email headers using both manual techniques and automated tools.

Prerequisites

  • Basic understanding of SMTP protocol and email delivery
  • Familiarity with DNS records (MX, TXT, SPF, DKIM, DMARC)
  • Python 3.8+ installed
  • Access to email client that can export raw headers (Outlook, Gmail, Thunderbird)

Key Concepts

Critical Header Fields

  1. Received: Chain of mail servers the message passed through (read bottom to top)
  2. From / Return-Path / Reply-To: Sender identity fields (often spoofed)
  3. Authentication-Results: SPF, DKIM, DMARC verification outcomes
  4. X-Originating-IP: Original sender IP address
  5. Message-ID: Unique identifier; anomalies indicate spoofing
  6. X-Mailer / User-Agent: Email client used to compose the message

Red Flags in Headers

  • Mismatched From and Return-Path domains
  • SPF/DKIM/DMARC failures in Authentication-Results
  • Suspicious Received chains with unfamiliar relay servers
  • X-Originating-IP from unexpected geographies
  • Missing or malformed Message-ID
  • Unusual X-Mailer values (e.g., mass-mailing tools)

Implementation Steps

Step 1: Extract Raw Email Headers

Gmail: Open email -> Three dots -> "Show original"
Outlook: Open email -> File -> Properties -> Internet Headers
Thunderbird: View -> Message Source (Ctrl+U)

Step 2: Parse Headers with Python

Use the scripts/process.py script to automate header analysis including IP geolocation, authentication validation, and anomaly detection.

Step 3: Validate Authentication Chain

  • Check SPF alignment: Does the sending IP match the domain's SPF record?
  • Check DKIM signature: Is the cryptographic signature valid?
  • Check DMARC policy: Does the message pass DMARC alignment?

Step 4: Trace Mail Route

  • Read Received headers from bottom to top
  • Map each hop's IP to organization/location
  • Identify unexpected relays or delays

Step 5: Correlate with Threat Intelligence

  • Look up originating IP on AbuseIPDB, VirusTotal
  • Check sending domain age on WHOIS
  • Search for known phishing infrastructure patterns

Tools & Resources

Validation

  • Successfully parse headers from 3 different email providers
  • Correctly identify authentication pass/fail status
  • Accurately trace email routing path
  • Detect at least 3 phishing indicators in a sample phishing email

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