What are email headers?

What are email headers?


Email header are a list of key pair value added to the beginning of email message that acts as metadata

They are specifying the:

  • where,
  • the who,
  • and the from.

The client will add headers that defines information about the message and every server will add at minimal the received header (other headers such as X-name can also be added).

They have the same and functionality than the html header because the email is just a part of the web.



Header fields are lines composed of:

  • a field name,
  • followed by a colon (“:”),
  • followed by a field body,
  • and terminated by CRLF (end of line)


An email full with headers where only the last line is not an header but the body

You can note that they follows the same format that an http message

Delivered-To: [email protected]
Date: Fri, 12 Jun 2020 21:08:18 +0200
To: [email protected]
Subject: Without hosts dkim test !
User-Agent: Heirloom mailx 12.5 7/5/10
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Message-Id: <[email protected]>
From: [email protected] (root)
cc: [email protected]
bcc: [email protected]

This is the body of the email


You can analyze them (ie format them) with the message header toolbox


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