Email Headers Explained: Understanding Email Header Information

There comes a time when you find yourself wanting to know more about an email you received. Maybe you are questioning its legitimacy, maybe you are curious of the authentication that took place before it ended up in your mailbox.

You can’t be too careful these days and sometimes you need answers you cannot simply receive by viewing the basic information provided. Sometimes you need to “View Full Headers”. If you have never looked into email headers, you may find this a bit daunting. But fret not! Here is a breakdown on how to read email header information.

Authentication-Results Header

This is where you can find what your email client authenticated when the email was sent. It will provide you with SPF and DKIM authentication. Here is an example of how to break down the code in the header that you might see:

1. spf=pass (sender IP is 65.54.190.161; identity alignment result is pass and alignment mode is relaxed);
2. [email protected];
3. dkim=none (identity alignment result is pass and alignment mode is relaxed)
4. header.d=account.microsoft.com;
5. x-hmca=pass [email protected]

You can see by reviewing this header information, the SPF authentication passed because the sender IP of 65.54.190.161 is allowed to send from account.microsoft.com. DKIM=none indicates that the message was not DKIM-signed.

Received

The received section is a list of all of the servers the message traveled in order to reach your mailbox. In order to read this information in the order it traveled, you will want to read from the bottom up. This means the first line in the “Received:” header should be your own mail system as that is the end of its journey.

From

The from field is who the message is sent from (header.from). This field can be easily forged and is why we suggest ensuring you only open email that has been authenticated. In our sample, the message passes SPF. This is a good sign of legitimacy. However, you still want to be cautious.

Return Path

The return path is the email address the sender would like you to use to reply to the email. This is the same as the Reply-To address.

Envelope-to

The email address that the email is intended to.

To

This displays who the message is addressed to, but may not contain the recipient's email address.

Message ID

The message ID is given to the message by the mail server when the message was first created. These ID’s can help track information and are easily forged by malicious senders.

Subject

Created by the sender, generally the high-level topic of the message being sent.

Real Example

This is a real example that was purported to be sent by a CEO to an intended recipient, but was actually from a spoofed email. While the sender's name and the company name look legitimate, if you look at the fields highlighted in yellow—specifically the From address which is written generically as <[email protected]> [with Gmail's domain being misspelled], a Reply-To address of "none", and the generic subject line of "Voice Mail", representing a fraudulent vishing attempt.