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

Received: Chain of mail servers the message passed through (read bottom to top)
From / Return-Path / Reply-To: Sender identity fields (often spoofed)
Authentication-Results: SPF, DKIM, DMARC verification outcomes
X-Originating-IP: Original sender IP address
Message-ID: Unique identifier; anomalies indicate spoofing
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

MXToolbox Header Analyzer: https://mxtoolbox.com/EmailHeaders.aspx
Google Admin Toolbox: https://toolbox.googleapps.com/apps/messageheader/
AbuseIPDB: https://www.abuseipdb.com/
VirusTotal: https://www.virustotal.com/
PhishTank: https://phishtank.org/

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