An email header contains information about who sent an email, to whom, when, how it got there, and so on. Most of this isn't critical to everyday email reading so email clients hide it. A full email header looks like this:

 Return-Path: <noreply@spammer.net>
 Delivered-To: user@company.com
 Received: (qmail 4584 invoked by uid 64014); 14 Nov 2003 23:38:27 -0000
 Received: from noreply@spammer.net by foo@company.com with AmikaGuardian-Server-2.0.0 (Processed in 2.524528 secs); 14 Nov 2003 23:38:27 -0000
 Received: from unknown (HELO isp.com) ([])
           (envelope-sender <noreply@spammer.net>)
           by mail12.spammer.net (qmail-ldap-1.03) with SMTP
           for <user@company.com>; 14 Nov 2003 23:38:21 -0000
 Received: from sc8-sf-netmisc.spammer.net ([]) by isp.com ; Fri, 14 Nov 2003 18:37:54 -0500
 Received: from sc8-sf-web4-b.spammer.net ([] helo=sc8-sf-web4.spammer.net)
 	by sc8-sf-netmisc.spammer.net with esmtp (Exim 3.36 #1 (Debian))
id 1AKnVV-0006cp-00; Fri, 14 Nov 2003 15:37:41 -0800
 Received: from nobody by sc8-sf-web4.spammer.net with local (Exim 3.36 #1 (Debian))
id 1AKnVV-0000pn-00; Fri, 14 Nov 2003 15:37:41 -0800
 To: noreply@spammer.net
 From: "Joe Spammer" <noreply@spammer.net>
 **Subject: [spam] RE: getting mail??  help!!!!**
 Mime-Version: 1.0
 Content-Type: text/plain; charset="ISO-8859-1"
 Message-Id: <E1AKnVV-0000pn-00@sc8-sf-web4.spammer.net>
 Date: Fri, 14 Nov 2003 15:37:41 -0800
 X-Rcpt-To: <user@company.com>
 **X-Text-Classification: spam**

Note: The three lines in bold were inserted (or modified) by POPFile before POPfile passed along the email to the mail client. For this example, both the X-Text-Classification header and the Subject line were modified. In practice, however, there is no reason you would have both features turned on at the same time.

See also:

glossary/header.txt · Last modified: 2008/02/08 19:49 (external edit)

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