Interpreting Email Headers: How to Check Email Headers And Why They Matter

Interpreting Email Headers: How to Check Email Headers And Why They Matter
18 April, 2022 • ... • 543 views
Irene Dmitrieva
by Irene Dmitrieva

Email headers are the behind-the-scenes data of an email that determine things like its routing, sender information, and more. Although this data is generally hidden from view, understanding how it works can be handy when troubleshooting email delivery issues or launching email campaigns.

In this article, we’ll give you a crash course in email headers, explaining what they are and how they work. We’ll also show you how to view and interpret headers.

What is an email header?

The header is a code that can be used to authenticate emails based on the data it contains.

Many mail recipients understand the header of the email as its subject line. This is only partially correct. In fact, the email header contains much more info connected with the emails transmission process — metadata.

Metadata includes data such as “from” and “to,” the type of content, the browser used to write the email, the delivery date, etc. We’ll touch on them below.

Take a look at the example below to get an idea of what your email header might look like.

Email Header Example

What are its main purposes?

Why do we need this metadata? Subscribers might not look into it, but email clients carefully analyze the data to shield their users from spam, phishing, and other dangers.

This is how the headers of the emails can be useful:

  1. Protecting mailboxes from malicious attacks. Despite all its simplicity and convenience, email is not safe. You can fall victim to phishing (attacks that steal confidential or sensitive info).
    The information in email headers can help to avoid spam. The “Received” tag and other parts of it, such as the timestamp or IP address get analyzed by email services to see if they should deliver this message or not.
  2. Find and fix problems. The headers can “tell” you a lot about where an email has been and what happens along the way. You’ll be able to tell if there were any errors or changes made along this path that might affect delivery.
    When you’re trying to figure out why an email hasn’t been reaching its destination, it can help tremendously if you take a look at the header. The info it holds can be useful for those who have a knack for tech-savvy to fix any problems and make sure future emails are delivered successfully.
  3. Email tracking. In addition to the most common identifiers (From, To, Date, Subject), email headers also provide details about the route that an email takes as it passes from one computer to another.
    Mail Transfer Agents (MTAs) facilitate email transfer. When an email is sent from one computer to another, it passes through an MTA. Each time a message is sent or forwarded by an MTA, it is stamped with the date, time, and recipient.
    In a sense, this is similar to how a post office would send a letter: every time a letter passes through the post office on its way or if it is forwarded, it gets stamped. In this case, stamps are the header of the email.

The delivery of your email is a key concern when it comes to successful campaigns. If you are looking to increase the likelihood of successful deliverability and email open rate, headers can be a valuable resource. This means that you should always check for any errors in the configuration before mailing anything important, and use testing tools if possible so as not to leave yourself without a chance of success.

How to read email headers

An email header is an invaluable tool for understanding your emails. The following are only some examples from the standard fields in an incoming or outgoing message.


The sender’s name and email address.

The From line in email header


The subject line of the letter as specified by the sender.

The Subject line in email header


The date and time of when this mail was sent out.

The Date line in email header


The addresses of the person or company being targeted. If there are multiple recipients, the email header will include all names and addresses of those who receive the message.

The To line in email header


Also known as Reply-To, the address of who will receive your reply.

The Return-path line in email header


A line similar to Reply-To, identifies that the email was sent to the recipient’s reply address.

The Envelope-To line in email header


This line displays the servers through which the email went before reaching the recipient’s mailbox. To read it in chronological order, read from the bottom (where the email was originally sent from) to top (the destination of the email or, in this case, your computer ).

The Received line in email header

DKIM-Signature & Domainkey-Signature

This is a signature that verifies the authenticity of the sender. With DomainKeys Identified Mail, the domain is linked to the sender’s address. In this way, the sender is responsible for their mailings.

The DKIM signature in email header


This is a message identifier code. It has a standard format and is a part of the email address.

The Message ID line in email header


Allows you to send attachments in various forms, for example, text, audio, visual content, and more.

The Mime-Version line in email header


Tells whether the email is in plain text or HTML format.

The Content-Type line in email header


Tells you if the email is spam or not.

The X-Spam-Status line in email header


Displays the spam rating, normally generated by your service or email client.

The X-Spam-Level line in email header

Message body

The main part of the email, the content.

Every email message always contains headers. The headers hold both the recipient’s and sender’s addresses. Depending on the email client, the email may contain a different set of headers. Some are required and some are used on rare occasions.

How to check email headers in different clients

The tech data in the header can be long and difficult to understand. Mail clients don’t show all this information to the recipient without need. But it can easily be found in a few clicks.


In all Google apps (including Gmail), the steps required to view technical header data are the same.

Open the email whose header you want to view and look for the vertical dots on the right. Then select Show Original from the dropdown menu.

How to check email header in Gmail

Here you can see the metadata:

How to see the metadata

Clicking on Download original, you get the code of the letter in EML file format, which from time to time is asked to send to developers. You can send it as an attachment.

Below you will see the code of the email, including the technical headers:

The code of the mail with header


As with Gmail, click the dots, only in the proposed menu select View → View message source:

Outlook message source


In this client, the algorithm is the same — click on the three dots, then → View raw message.

View raw message in Yahoo

Apple Mail

Open the message and find the View menu item. Choose the Message field. The headers can be viewed under the All Headers option.

Email header preview in Apple Mail


To check the email message header in Mozilla Thunderbird, click the View menu. You can then select either Headers→All or the Message Source option.

Email header preview in Mozilla Thunderbird


In the MailSpring client, clicking on the chevron next to Reply will show you all of your message’s headers.

View email headers in MailSpring
Source: Mailspring Community


The email headers are an important part of every message that determines where it goes, who sent it, and more. Although this data is generally hidden from view, checking an email header will help you avoid phishing attacks by protecting yourself from malicious emails.

Understanding how headers work can be handy when troubleshooting email delivery issues, and tracking down spam emails. They may provide insight into its deliverability. Becoming familiar with these elements can help you launch successful campaigns whose results you can measure.

18 April, 2022
Article by
Irene Dmitrieva
As a marketing copywriter, I have experience creating compelling content for websites and social media posts. My background in market research helps me ensure that my copy is both on-brand and data-driven. I am excited to bring my skills and experience to Selzy team and help drive success for this company.
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