What are email headers?

What are email headers?


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

They specify the:

  • where: recipient,
  • the who: the sender,
  • and the from: the author


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

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


Who adds them?

  • The client will add headers that defines information about the message
  • Every server will add for tracing:


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)


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


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