What Is An Email Header?

The Warmup Inbox Team
The Warmup Inbox Team

An email header is a short string of code that’s used to authenticate an HTML message.

You’ve heard all about how essential it is to have a snappy email subject line in email marketing. You know that it’s crucial to have your “from” address clearly state your company’s name or a person’s name. You know that without warming up your inbox, you could end up in junk folders.

So what’s an email header, and why haven’t we talked about them before? Can we go about business as usual without bothering with email headers?

What Is An Email Header And What Do They Do?

Email headers are more than just the addresses, date, and subject section of a message. An email header is a short string of code that’s used to authenticate an HTML message. The header always comes before the email body.

Email headers serve three purposes:

  • Providing information about who sent the message and who is supposed to receive the message
  • Preventing spam and phishing attacks
  • Tracking the email route

When a recipient gets a message, they can use the email header to ensure that it isn’t spoofed. The person receiving the message can also use the header to verify that the email is safe before clicking on links within the message.

As the person running an email marketing campaign, you should care about your email headers because they play a vital role in getting your message into your recipients’ inbox.

Since every email has a header, mail transfer agents (MTAs) will use the header to determine whether or not the message is coming from the person it says it’s coming from. If an email has been sent to other addresses before reaching the intended recipient, the MTA will flag it as suspicious to prevent their user from a potential cyberattack.

Headers are comprised of a string of metadata that shows the message’s journey from the moment the initial sender clicked send. Marketing teams can run tests to determine what security protocols they need to implement to get their messages out of spam folders and into inboxes.

How To Find An Email Header

Finding an email header is similar across all email platforms, but each provider has a somewhat unique process. We’ll review how to look at email headers for the most popular platforms, but be sure that you’re looking at a message from the recipient’s perspective.

How to View an Email Header On Gmail

Gmail takes advantage of machine learning to create a platform that gives users a nearly spam-free inbox. Understanding what your header looks like to Gmail can help you tweak your header to maximize your chances of getting into the primary inbox.

  1. Click on the vertical three-dot icon to the right of the reply button on a message
  2. Click “Show original” from the drop-down menu; this will take you to an overview of the information in the message
  3. At the bottom of the form, you can click on “Download original” to get the header or click on “Copy to clipboard” to paste it somewhere else

How to View an Email Header on Microsoft Outlook

Microsoft accounts are the most targeted platforms for cybercrime, so customers may be more likely to check the email header for a message coming in from an unrecognized sender.

  1. Click on the horizontal three-dot icon to the right of the forward button on a message
  2. Hover over “View” on the drop-down menu
  3. Click on “View message source” at the bottom of the drop-down menu under “View”

How to View an Email Header on Yahoo

  1. Click on the horizontal three-dot icon next to the “Spam” button at the top of an email
  2. Click “View raw message” from the drop-down menu

How to View an Email Header on Mozilla Thunderbird

  1. Click on the horizontal three-line icon in the top right corner of a message
  2. Click on “View” to see another menu
  3. Click on “Headers” under the View menu
  4. Select “All” from the Headers menu

On Thunderbird, you can simply cress Control+U when you open the email, but it shows a lot more information than just the header, which can be confusing if you’re unsure what to look for.

How to View an Email Header on iCloud Mail

For the browser application:

  1. Click on the Gear icon on a message
  2. Click on “Show Long Headers”

For the Mac Mail Application:

  1. Open the message, then click on “View” on the top toolbar
  2. Hover over “Message” on the View drop-down menu
  3. Click on “Raw Source” on the Message drop-down menu

How to View an Email Header on Zoho Mail

  1. Click on the v-shaped icon to the right of the forward button on a message
  2. Click on “Show original”
  3. At the top of the content, you can click on “Download full content,” “Copy to clipboard,” or “Show full content”

How to View an Email Header on AOL

  1. Click on the “More” button above the subject line
  2. Click on “View Message Source,” which will open a new window with the header

How To Understand Email Headers

Now that you’ve downloaded the raw metadata, the next task is to interpret the information in front of you.

Let’s break down the different tags you’re likely to see in the email header’s metadata.

  • From: Shows who the sender is
  • To: Shows the intended recipient, including those carbon copied (CC) and blind carbon copied (BCC)
  • Subject: Shows what you wrote in the subject line
  • Return Path or Reply-To: The email address that a reply email is sent to
  • Envelope-To: Shows who the email was sent to
  • Date: Timestamp of when an email was sent, usually in day, dd month yyyy hh:mm:ss format (Tues, 12 Oct 2021 12:03:21)
  • Received: Shows the email address of the recipient and all other addresses the email passed through on its way to the recipient
  • DKIM Signature and DomainKeys: Shows signatures to help ISPs authenticate the senders by connecting the domain name with the email
  • Message-ID: A unique string of letters and numbers automatically generated when an email is written
  • MIME Version: Shows the Multipurpose Internet Mail Extensions (MIME) version used to extend an email’s format and functionality
  • Content-Type: Shows whether an email is text-only or uses HTML
  • X-Spam-Status: Gives the spam score of an email and whether it was flagged as spam
  • X-Spam-Level: Shows an asterisk for every spam point an email gains

Do Email Headers Matter?

Email headers are vital for your email deliverability rate. Especially when launching a cold email campaign, you want to ensure that the email headers are clean and accurate, so you don’t end up in any spam folders.

Like so many other email safety protocols, headers are another tool that recipients and ISPs have to prevent malicious attacks. The best thing you can do for your email reputation and deliverability rate is to implement DKIM to help authenticate your message.

Running tests to view your email headers can help you understand why some of your messages may be going to spam and give you guideposts to figure out how to get back on track. Before you launch a massive campaign, send out a preliminary email to make sure that the information contained in the header is correct.

The more you do to keep your recipients safe, the better your domain reputation and the more inboxes you’ll land in. Monitoring email headers are just another piece of the deliverability puzzle, and they serve as an excellent tool for improving your email campaigns.

For more helpful tips and tricks to boost your team’s deliverability rate, visit our blog.