Почему письма с моего почтового сервера попадают в спам у google?

заголовки письма

Delivered-To: sergey@shukan.ru
Received: by 10.216.164.130 with SMTP id c2csp169668wel;
Tue, 17 Dec 2013 21:59:42 -0800 (PST)
X-Received: by 10.152.120.231 with SMTP id lf7mr10588261lab.36.1387346381781;
Tue, 17 Dec 2013 21:59:41 -0800 (PST)
Return-Path:
Received: from mailserver.ru (mailserver.ru. [mailserver-ip])
by mx.google.com with ESMTP id k8si8652639lag.49.2013.12.17.21.59.41
for ;
Tue, 17 Dec 2013 21:59:41 -0800 (PST)
Received-SPF: pass (google.com: domain of no-reply@mailserver.ru designates mailserver-ip as permitted sender) client-ip=mailserver-ip;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of no-reply@mailserver.ru designates mailserver-ip as permitted sender) smtp.mail=no-reply@mailserver.ru;
dkim=pass header.i=@mailserver.ru
Received: from localhost (mailserver.ru [127.0.0.1])
by mailserver.ru (Postfix) with ESMTP id B0DCAA36A4
for ; Wed, 18 Dec 2013 16:59:38 +1100 (SAKT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mailserver.ru; h=
content-type:content-type:content-transfer-encoding:mime-version
:x-mailer:message-id:subject:subject:from:from:to:date:date; s=
dkim; t=1387346370; x=1388210370; bh=YMJpxeaNZgh0ypmL+uqiQXqFtUG
mxA3avqq4ShFdhfw=; b=gO342m5gT3KCAONAxZgJ1AGfQuAGPjnB/jmkxg3Numd
0MjI4BRlu69I6FDN8Vja/iHs1FE55J30Ud9qRwDMTIbKsbuqLcpH/V/x1ArtYOWD
mSZz32IPYcD5MeuvKZJcH7E78QXU31fy9wtsSBgZ8keIYPCKJZp1pm8AEtJ386LY
=
X-Virus-Scanned: Debian amavisd-new at mailserver.ru
Received: from mailserver.ru ([127.0.0.1])
by localhost (mailserver.ru [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id pGevwjk64PAT for ;
Wed, 18 Dec 2013 16:59:30 +1100 (SAKT)
Received: from forum.XXXXX.ru (XXXXX.ru [forum-ip])
by mailserver.ru (Postfix) with ESMTPSA id 7E71BA369F
for ; Wed, 18 Dec 2013 16:59:25 +1100 (SAKT)
Date: Wed, 18 Dec 2013 16:59:24 +1100
To: sergey@shukan.ru
From: =?utf-8?B?0JDQodCi0JIg0J7QsdGK0Y/QstC70LXQvdC40Y8=?=
Subject: =?utf-8?B?0JLQvtGB0YHRgtCw0L3QvtCy0LvQtdC90LjQtSDQsNC60LrQsNGD0L3RgtCw?=
=?utf-8?B?IFNodWthbg==?=
Message-ID:
X-Priority: 3
X-Mailer: PHPMailer 5.1 (phpmailer.sourceforge.net)
Errors-To: no-reply@mailserver.ru
Sender: no-reply@mailserver.ru
MIME-Version: 1.0
Content-Transfer-Encoding: 8Bit
Content-Type: text/plain; charset="utf-8"