Email Header Definition and Details

You may need to view an email's headers during troubleshooting

Email marketing and many envelopes in smartphone screen
Busakorn Pongparnit / Getty Images

Although you rarely see the complete email header of an email, it contains routing information that is indispensable for delivering a piece of digital mail to the proper recipient. Email headers can also play an important role in allowing email server administrators to troubleshoot routing issues.

The Role Email Headers Play

Every email consists of two parts: the header information and the body of the message. Email header lines contain behind-the-scenes information that makes up the first part of an email message; they control the transmission of the message as well as metadata including the subject, origin and destination email addresses, the path an email takes, the servers it passes along the way, the time it did so, and the priority of the message.

Equipment in server room
Headers can show what computers your email passed through before arriving on your machine. Erik Isakson / Getty Images

Header lines are normally not displayed by email programs or web pages. Only certain information — the subject line, sender and sent date—is displayed and formatted for easy use. Optionally, the Cc and Bcc fields can be displayed; they are also included in the headers.

Why View an Email Header

Most people never need to view the complete email header lines of an email. However, you may be asked by a technician during troubleshooting an email problem to send the complete headers for evaluation, or you may be able to use them to identify a spam sender or verify the email is a spoof or phishing attempt.

How to View an Email Header

Screenshot showing how to show original email in Gmail
Michael Archambault

Email headers are not particularly friendly to the untrained eye, and the header is often longer than the email itself. Most email clients and email web pages provide a way for you to display the email headers if you are curious.

Here are some of the most common email providers and how you can view an email's header:

Outlook: Open Email > Select Actions > Select View message source.

Gmail: Open Email > Select More (three vertical dots) > Select Show original.

Yahoo: Open Email > Select More (gear icon) > Select View Raw Message.

iCloud: Open Email > Select Actions (gear icon) > Select Show Long Headers.

AOL: Open Email > Select Action > Select View Message Source.

Understanding an Email Header

Email headers can appear as long complex blocks of information, but a little bit of information can help you search email headers like a professional. Within an email header, there are different bits of data as shown below:

Date: Tue, 27 Nov 2018 15:47:41 -0500
From: Michael Archambault <XXX@XXX.com>
To: Michael Archambault <XXX@XXX.com>
Message-id: <XXX@XXX.com>
Subject: Meeting for lunch?
X-Mailer: Airmail (528)
MIME-version: 1.0
Content-type: multipart/alternative;
--5bfdad6d_30895304_11a
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Want to meet for lunch today at Good Burger?
-Michael Archambault
--5bfdad6d_30895304_11a
Content-Type: text/html; charset="utf-8"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

This is only a partial email header shown as an example — the original header is about 9x longer. Additionally, any personal email addresses or private information has been removed and replaced by the X symbol.

Content-Type: Notes whether the email is HTML or plain text.

Date: When the email was composed.

Delivery Date: When the email was received by your mail server.

From: Who sent the email.

Received: All of the servers the email was sent through.

Return-Path: Where a reply to the email will be sent.

Subject: The email's subject.

To: Whom the email was addressed.

X-Originating-IP: The IP address from which the email was sent.

X-Spam: Spam information generated by your email service.

Email header information can be forged; it is critical that only sections containing the keyword Received be fully trusted. Some fields such as From can be easily manipulated.

Fighting Spam with Email Headers

Phishing attempts are malicious attacks that attempt to have us hand over private or sensitive information to an individual masquerading as an authentic source such as your bank or other financial institution. Examining headers can be a powerful way of identifying such scams and keeping yourself safe.