What Is an Email Header? A Comprehensive Guide
By Emil Kristensen CMO
@ Sleeknote

Email is an essential communication tool that we use for various purposes – from personal to professional. However, have you ever taken a closer look at the email header? Most of us tend to overlook it and focus only on the message content. But, the email header contains a wealth of information that can help you understand the context of the email, and identify security threats and spam. In this comprehensive guide, we will discuss the email header components, their importance, and how to view, modify, and customize them.

The Components of an Email Header

The email header contains several components, including the following:

  • From: This is the sender’s email address.
  • To: This is the recipient’s email address.
  • Date: This is the date and time the email was sent.
  • Subject: This is the brief description of the email content.
  • CC: This is the list of carbon copy recipients.
  • BCC: This is the list of blind carbon copy recipients.
  • X-Mailer: This is the email client or server used to send the email.
  • X-Originating-IP: This is the IP address of the sender’s email client or server.

The Importance of Email Headers in Communication

Email headers are vital in understanding the context of the email. For example, the sender’s email address can tell you if the sender is a known or trusted entity. The date and time of the email can help you identify if it is an urgent or time-sensitive message. The X-Originating-IP component can help you determine the sender’s physical location and if it matches the sender’s claimed location. All of these components combined can help you decide how to respond to the email and whether to take any action.

How to View the Email Header in Different Email Clients

Viewing the email header is simple, although the process may differ slightly depending on the email client you are using. In most email clients, you can view the email header by right-clicking on the email and selecting “View Message Source” or “Show Original.” This will open a new tab or window with the email header information. In Gmail, you can click on the three dots in the top right corner of the email, then click “Show Original.” In Outlook, you can click on the three dots in the top right corner of the email, then click “View Message Details.”

Understanding IP Addresses and Domain Names in Email Headers

IP addresses and domain names are critical in email communication. The sender’s IP address can help you determine their location and whether it matches the claimed location. Sometimes, the domain name can give you an indication of the company or organization where the email originated. However, both IP addresses and domain names can be spoofed or faked, making them less reliable as a security measure.

Analyzing Email Headers for Security Threats and Spam Detection

Aside from understanding the context of an email, email headers can also help you identify security threats and spam. For example, if an email claims to be from a legitimate company, but the IP address or domain name does not match the company’s official records, it could be a phishing attempt. If an email is from an unknown sender and contains suspicious attachments or links, it could be malware. By analyzing the email header components, you can identify these threats and take the appropriate action.

How to Modify and Customize Your Email Header Settings

You can modify and customize your email header settings in some email clients. For example, in Gmail, you can change the default reply-to address, add a signature, or change the default email language. In Outlook, you can customize the message format, add voting buttons, and use message templates. However, keep in mind that modifying any email header components can impact the email’s integrity and affect its delivery and reception.

Best Practices for Writing Effective Email Headers

Writing an effective email header can help you increase the chances of your email being read and acted upon. Here are some best practices:

  • Be specific: Use a concise and specific subject to describe your email content.
  • Avoid using all caps or excessive punctuation: They can make your email look unprofessional.
  • Keep it short: Don’t use more than eight to ten words in your subject line.
  • Personalize the sender name: If sending from a business email address, include your name or title to give the email a personal touch.

Common Mistakes to Avoid in Email Header Formatting

Email header formatting is essential to ensure the email delivery and readability. Here are some common mistakes to avoid:

  • Leaving the subject line empty: An empty subject line can give the impression of a spam email.
  • Using long and convoluted subject lines: Long subject lines can make it difficult to read or understand the email’s content.
  • Using special characters: Special characters like %, &, and @ can trigger spam filters and affect email delivery.
  • Sending emails with inconsistent or incomplete information: failing to include essential email header components, such as the subject line, can lead to confusion and prevent the email from delivering altogether.

The Future of Email Headers: Emerging Trends and Technologies

Email technology is continuously evolving to enhance communication, security, and privacy. Some emerging trends and technologies in email headers include:

  • DMARC: DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an email validation system designed to detect and prevent email spoofing.
  • Encryption: Email encryption is becoming more common as a way to secure email communication and protect sensitive information.
  • Artificial intelligence and machine learning: AI and machine learning can help detect and block spam and phishing emails by analyzing email header components and content.


The email header is often overlooked, but it is a vital component of email communication. Understanding the components and analyzing them can help you determine the context of the email and identify security threats or spam. Now that you have a comprehensive guide on email headers, you can use this information to improve your email communication, security, and privacy. Remember to follow the best practices and avoid common mistakes in email header formatting, and stay updated on the emerging trends and technologies in email headers.