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What Are Email Headers

Email headers are found at the beginning of each email. They contain detailed information about the sender of the email and to whom it is delivered in addition to other details used by the sending and receiving email software in an attempt to validate that the message is valid and not spam.

What is contained in email headers?

In the headers you'll find things such as who the email is delivered to, when the email was received, the return path (reply to), the SPF received status (pass, fail, etc.) and much more. See RFC 822 for more information.

An example of an email header is found below.

Delivered-To: example@unlocktheinbox.com
Received: by with SMTP id sdk88d8fuzl;
        Mon, 30 May 2011 00:07:07 -0700 (PDT)
Received: by with SMTP id sdk88d8fuzl.222.5465455621259;
        Mon, 30 May 2011 00:07:06 -0700 (PDT)
Return-Path: <example@senderdomain.com>
Received: from server.senderdomain.com (server.senderdomain.com [])
        by example.unlocktheinbox.com with ESMTP id dsdf89sksdjfa8.52.2011.;
        Mon, 30 May 2011 00:07:05 -0700 (PDT)
Received-SPF: pass (unlocktheinbox.com: domain of example@senderdomain.com designates
              as permitted sender) client-ip=; Authentication-Results: 
              example.unlocktheinbox.com; spf=pass (unlocktheinbox.com: domain of 
              example@senderdomain.com designates as permitted sender) 
              smtp.mail=example@senderdomain.com; dkim=pass (test mode) 
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=s1024; d=senderdomain.com;
DomainKey-Signature: a=rsa-sha1; c=nofws; q=dns; s=s1024; d=senderdomain.com;
Received: by example.senderdomain.com (PowerMTA(TM) v3.5r15) id asdf44asdf44 for
           Mon, 30 May 2011 00:07:02 -0700 (envelope-from <example@senderdomain.com>)
MIME-Version: 1.0
Content-Disposition: inline
Content-Transfer-Encoding: base64
Content-Type: text/plain
X-Mailer: MIME::Lite 3.023 (F2.74; T1.26; A2.04; B3.07; Q3.07)
Date: Mon, 30 May 2011 00:07:03 -0700
From: senderdomain.com <example@senderdomain.com>
To: example@unlocktheinbox.com
Subject: This is a test email. None of these values are real.
Errors-To: example@senderdomain.com
X-Reminder-To: R
X-Reminder-Processor: Summarized
X-Original-Sender: example@senderdomain.com
Message-ID: <0.4.45.cB8.dfs445wcc5ddzf.7@example.serverdomain.com>

How Do I View Email Headers?

Email headers are not typically displayed by default. Depending on your email client, you may need to do one of the following:
  • Press the reply button
  • Apple Mail - Open the email and then choose Messages > Long Headers from the View menu.
  • Outlook - Open the email and select Options from the View menu
  • Outlook Express - Open the email and select Properties from the File menu. The email headers are displayed in the Message Properties panel of the Details tab
You can also send an email to "mailtest@unlocktheinbox.com" which will respond to your email with a full analysis of your email headers.

Source: Unlock The Inbox

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