Email headers are the technical details that come attached to every email. They include information such as the email's sender, recipient, subject, and more. Understanding email headers is essential for verifying email authenticity, enhancing security, and detecting phishing attempts. In this guide, we will explore what email headers are, dissect their anatomy, and explain the common fields you should look for when analyzing an email header.

Table of Contents +

What Are Email Headers?

Email headers are blocks of metadata attached to every email you send or receive. Unlike the visible content of an email, which contains the actual message, headers contain technical information that details the email's journey from the sender to the recipient. This includes data like the sender's IP address, the servers the email passed through, and authentication results.

Understanding email headers is crucial because they provide transparency into the email's path and origin. This information is invaluable when determining whether an email is legitimate or part of a phishing attempt [1].

Anatomy of an Email Header

The anatomy of an email header is composed of various fields, each serving a specific purpose. Understanding these fields allows you to trace the email's path, verify its legitimacy, and detect any anomalies that might indicate fraudulent activity.

Here is a breakdown of the key components of an email header:

1. Received

The Received fields are the most crucial parts of an email header. Each time an email passes through a mail server, a new "Received" header is added. These headers are listed in reverse chronological order, with the most recent server information appearing first. By reading these fields, you can trace the path an email took from the sender to your inbox.

Example:

Received: from mail.example.com (mail.example.com [192.0.2.1])
        by smtp.gmail.com with ESMTPS id abc123
        for <[email protected]>; Mon, 19 Sep 2024 12:00:00 -0700 (PDT)

How to Use: Start from the bottom-most "Received" header and move upwards to trace the email's origin.

2. From

The From field indicates the sender's email address. While it shows who the email is purportedly from, it's important to note that this field can be spoofed. Therefore, additional verification is necessary to confirm the sender's identity.

Example:

From: John Doe <[email protected]>

3. To

The To field shows the recipient's email address. This helps confirm who the email was intended for.

Example:

To: [email protected]

4. Subject

The Subject field contains the subject line of the email. While it gives an overview of the email's content, it's not used for verification purposes.

Example:

Subject: Meeting Reminder

5. Date

The Date field shows when the email was sent. This can help determine if the email is timely or potentially delayed, which might be suspicious.

Example:

Date: Mon, 19 Sep 2024 12:00:00 -0700

6. Message-ID

The Message-ID is a unique identifier assigned to each email. It helps in tracking and referencing specific emails, especially in conversations and threads.

Example:

Message-ID: <[email protected]>

7. Return-Path

The Return-Path field specifies where bounce messages (non-delivery receipts) are sent. If the domain in the Return-Path differs from the sender's domain, it might indicate spoofing.

Example:

Return-Path: <[email protected]>

8. Authentication-Results

The Authentication-Results field displays the results of various email authentication checks, including SPF, DKIM, and DMARC. These protocols help verify that the email is legitimate and not spoofed.

Example:

Authentication-Results: mx.google.com;
    dkim=pass [email protected];
    spf=pass (google.com: domain of [email protected] designates 192.0.2.1 as permitted sender) [email protected];

How to Use: Ensure that all authentication checks pass. Failing any of them could indicate a fraudulent email.

9. MIME-Version and Content-Type

The MIME-Version and Content-Type fields define the format and type of content within the email, ensuring proper rendering by email clients.

Example:

MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8

10. Other Important Fields

Some additional headers may provide further details:

  • X-Mailer: Identifies the email client used to send the email.
  • List-Unsubscribe: Provides a method to unsubscribe from mailing lists.
  • Custom Headers: Used for specific purposes by email services.

Conclusion

Understanding and analyzing email headers is a powerful way to enhance your email security. By dissecting the various fields within an email header, you can verify the authenticity of messages, trace their origins, and protect yourself from potential threats like phishing and spoofing. Utilize tools like Email Header Analyzer to simplify this process and ensure your inbox remains secure.