Technical
Email Headers Explained: Reading the Hidden Metadata
Alex Chen
December 8, 2025
A comprehensive guide to understanding email headers and what they reveal about message origin and authenticity.
Introduction
Every email carries hidden information in its headers that tells the complete story of its journey from sender to recipient.
Essential Header Fields
From, To, and Date
From: John Smith <john@example.com>
To: recipient@example.com
Date: Sun, 22 Dec 2025 10:30:00 -0500Message-ID
A unique identifier for tracking and threading:
Message-ID: <unique-id-12345@mail.example.com>Tracing Email Path: Received Headers
The most valuable headers for tracing an email's origin:
Received: from mail-out.example.com [192.0.2.1]
by mx.recipient.com with ESMTPS
for <recipient@recipient.com>
Sun, 22 Dec 2025 10:30:05 -0500Reading tip: Read from bottom to top (oldest to newest)
Authentication Headers
| Header | Purpose |
|---|---|
| Received-SPF | Sender IP authorization |
| DKIM-Signature | Cryptographic verification |
| Authentication-Results | Combined results |
Conclusion
Email headers are a powerful tool for understanding email behavior. Whether investigating suspicious emails or troubleshooting delivery issues, knowing how to read headers is essential.