Why do emails go to spam?

Question

Exim

Registered a new domain, added it to our server.
According to spam databases, neither the domain nor the server are listed. Dkim/Spf are configured correctly.
But letters, even those written by hand through Roundcube, fall into spam immediately.
Where to dig a solution to this problem?

Received: from mxfront1h.mail.yandex.net ([127.0.0.1])
by mxfront1h.mail.yandex.net with LMTP id eZDmpx09
for yandex .ru>; Sun, 3 Apr 2016 20:40:36 +0300
Received: from unknown (unknown [2a03:f480:1:19::42])
by mxfront1h.mail.yandex.net (nwsmtp/Yandex) with ESMTPS id 7E2ULAty32-eZYmkRPo ;
Sun, 03 Apr 2016 20:40:35 +0300
(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
(Client certificate not present)
Return-Path: [email protected]
X -Yandex-Front: mxfront1h.mail.yandex.net
X-Yandex-TimeMark: 1459705235
Authentication-Results: mxfront1h.mail.yandex.net; spf=softfail (mxfront1h.mail.yandex.net: transitioning domain of .ru does not designate 2a03:f480:1:19::42 as permitted sender) [email protected]; dkim=pass [email protected]
X-Yandex-Spam: 4
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=optcosmetic.ru; s=dkim;
h=Message-ID:Subject:To:From:Date:Content-Transfer-Encoding:Content-Type:MIME-Version; bh=IcaJwWCBUlakQYYi9kfUc0uMVz/dZqH889ncE9zBqsw=;
b = XY / xF5ZXOxEHzMOlk3UZK + oVjO8oCRlrn03CJ9jQxhs + vMBh9xCTnxcvyDZbPPbMh7pT + hbydK9hkXSlsDSbUgyI81g4gBPA21CoJaKm9ZYH4miQZAVyeJ7psIE9m8whf / ETx8HZYR7HcQDTtiUzF1yfiwnA5opi7wgSJwUv / W4 =;
Received: from localhost ([127.0.0.1] helo=5.45.124.164)
by .ru with esmtpa (Exim 4.72)
(envelope-from .ru>)
id 1amm0p-00041b-CJ
for yandex .ru; Sun, 03 Apr 2016 20:40:35 +0300
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
format=flowed
Content-Transfer-Encoding: 8bit
Date: Sun, 03 Apr 2016 20:40:35 +0300
From: [email protected] To
: yandex.ru
Subject: =?UTF-8?Q?=D0=9F= D1=80=D0=BE=D0=B2=D0=B5=D1=80=D0=BA=D0=B0=20?==
?UTF-8?Q?=D1=81=D0=B2=D1= 8F=D0=B7=D0=B8?=
Message-ID: <[email protected]>
X-Sender: [email protected]
User-Agent: Roundcube Webmail/1.0.8
X-Scanned-By: ClamAV 0.99; Sun, 03 Apr 2016 20:40:35 +0300
X-Yandex-Forward: 11c17b19ee9a824729a1ded9819f0010
X-Yandex-Filter: 309920

Answer 1

Authentication-Results: mxfront1h.mail.yandex.net; spf= softfail (mxfront1h.mail.yandex.net: transitioning domain of .ru does not designate 2a03:f480:1:19::42 as permitted sender )

Add an entry to spf for ipv6 or tell the server to work only on ipv4.
Also check the correctness of the PTR record (reverse zone).

Answer 2

start with mxtoolbox.com/diagnostic.aspx
then check IP against blacklist databases