Email Headers Unraveled: What They Are and Why They Matter

An email has become one of the most common ways for people to communicate, and the use of email continues to grow. According to a recent report by Statista, users around the globe send and receive about 347 billion emails a day. At the same time, in December 2021, about 45% of emails were considered spammy. One of the ways to detect dangerous emails is with the help of information included in email headers. Read this article to learn what an email header is and how it can help you fight spam.

What Is an Email Header?

An email header is the section of an email message that contains metadata about the email. The header is located at the top of the email message, and it is typically not visible to the recipient unless they choose to view it. 

When you open any email in your inbox, you can see some of the data about the message such as From, To, Subject, and Date, and this information looks like this:

If you want to get more data, you should search for the email header in the settings. The same header you saw in the picture above will turn into something like this:

As you can see in the screenshot above, the email header is composed of several elements, each of which provides important information about the message. Here is a more detailed description of the main components:

• From: This field shows the email address of the sender. It is crucial to check this field carefully as spammers often fake the sender's email address and make it similar to the original one. 
• To: It displays the recipient's email address. However, if you are part of a group email, you will only see your email address here.
• Subject: It indicates the topic of the email. It is the first thing a recipient sees when they receive an email, so it should be a clear and concise summary of the email's content.
• Date: This field shows when the email message was sent. The format is usually the same: day, dd month, yyyy hh:mm:ss.
• Message ID: Message ID is a unique identifier assigned to each email message. This ID can help identify and track the email if it gets lost or delayed in transit.
• Reply-to: This field is optional and it displays the email address that the recipient can use to reply to the email. It’s not always the same as the sender's email address and can be set to a different email address for various reasons.
• Return-path: This field is the email address that is used to handle non-delivery reports. It is sometimes referred to as the bounce-back address.
• Envelope-To: This component is usually hidden in most email clients, as it is used by email servers to route incoming emails to the correct inbox. This field shows the email address to which the server should deliver the message.
• DomainKeys and DKIM Signatures: DomainKeys Identified Mail (DKIM) and DomainKeys are email authentication methods that verify the email's sender's domain name. Both methods are designed to help reduce the amount of spam. 
• Content-type: This field indicates the format of the email, such as plain text or HTML. This information is vital as it helps to display the email's content correctly in the recipient's email client.
• MIME version: It shows the version of the Multipurpose Internet Mail Extensions (MIME) protocol that was used to send the email message. MIME is the standard for sending multimedia content, such as images or videos, in email messages.
• X-Spam-Status: This field indicates whether the email is considered spam. It can be used by email clients or filters to sort emails into folders or take other actions based on the emails’ statuses.
• X-Spam-Level: This component is connected to the previous one and is usually indicated by a series of asterisks. The more asterisks an email gets, the higher the level of spam is.
• Message Body: The message body is the actual content of the email that is visible to the recipient. 

Understanding the email header and being mindful of its components can help you stay safe and make informed decisions when using email.

Why Email Headers Are Important

Email headers are vital for several reasons:

1. Email Routing and Delivery Verification. Email headers provide crucial information about the email's origin (for example, the servers the email passed through before reaching the recipient's inbox). This information can help you identify if the email is legitimate or if it was intercepted or modified along the way. For example, you may notice a delay in receiving an email or see that it was routed through some questionable servers. 
2. Sender Authentication. Email headers can also help verify the authenticity of the email's sender. This is particularly important in preventing email spoofing and phishing scams, as attackers usually try to impersonate a trusted sender to trick the recipient into following a dangerous link. Sender authentication methods, such as DKIM and DomainKeys, use digital signatures and cryptographic keys to validate the sender's domain name, and this information can be viewed in the email header. Check these fields to ensure that the email is from a legitimate source.‍
3. Troubleshooting: Email headers can also be useful in troubleshooting email delivery issues: bounced messages, undelivered messages, and other problems. If you review the email header and understand its contents, you can also identify such issues as incorrect email addresses or server issues, and take some action to solve the problem. However, if you want to analyze the performance of the whole campaign and not just one particular email, think about using a postmaster tool instead.

How to Find an Email Header in Various Email Clients

The process of viewing email headers can vary a bit depending on the email client you use. Let’s go over the most popular email clients.

Gmail

Open the email and click the three dots in the upper-right corner.

Select "Show original" to view the email header.

After that, you’ll be taken to a separate page with all the data you need.

Outlook

Open the email and click the three dots in the upper-right corner.

Select "View" and then choose “View message source” to see the email header.

Apple Mail

Open the email message and select "Develop" from the menu. 

Select "Show Page Source" to view the email header.

Wrapping Up

Email headers are a vital part of the email because they contain critical information about the sender, recipient, and other essential elements of the email. Email headers may be beneficial for identifying spam, verifying the authenticity of an email, and troubleshooting email delivery issues. Although the process of viewing email headers may vary based on the email client, the underlying information remains the same.