Complete message received by Gmail (email, server ip and host are replaced):
Delivered-To: <myemail> Received: by 10.180.24.132 with SMTP id u4cs216052wif; Thu, 20 Oct 2011 03:22:03 -0700 (PDT) Received: by 10.14.9.165 with SMTP id 37mr1294749eet.51.1319106122223; Thu, 20 Oct 2011 03:22:02 -0700 (PDT) Return-Path: <www-data@<serverdomain>> Received: from <serverdomain> (<serverdomain>. [<serverip>]) by mx.google.com with ESMTP id s55si2781134ees.156.2011.10.20.03.22.02; Thu, 20 Oct 2011 03:22:02 -0700 (PDT) Received-SPF: pass (google.com: domain of www-data@<serverdomain> designates <serverip> as permitted sender) client-ip=<serverip>; Authentication-Results: mx.google.com; spf=pass (google.com: domain of www-data@<serverdomain> designates <serverip> as permitted sender) smtp.mail=www-data@<serverdomain> Received: by <serverdomain> (Postfix, from userid 33) id AEF1F47462EE; Thu, 20 Oct 2011 10:22:00 +0000 (UTC) To: <myemail> Subject: Registration confirmation From: <sitename> mailing robot <no-reply@<serverdomain>> MIME-Version: 1.0 Content-type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit Message-Id: <20111020102200.AEF1F47462EE@<serverdomain>> Date: Thu, 20 Oct 2011 10:22:00 +0000 (UTC) Please confirm your registration on the site by clicking this link: <A href="<confirmationlink>" target=_blank><confirmationlink></A>
What's wrong with this e-mail? Why does Gmail think it is spam?