What are email headers?
They are specifying the:
- the who,
- and the from.
They have the same and functionality than the html header because the email is just a part of the web.
- the address
- the dkim
- the Received (for the routing)
- the user-agent (the client)
- the message id
- the return-path for bounce message
- and more
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