Letters (notifications) do not reach users, what could be the problem?

Question

Email

There was a problem, all letters (notifications) coming from the site do not reach users. And they return back to the box, also getting into SPAM.
I use sending letters with domain binding to Yandex mail, everything worked fine. From the box there are only notifications about the password during registration, new messages, topics. All in all, nothing like basic alerts without a bunch of spammy links. All these letters either end up in spam, or do not reach users at all, and the following response is returned:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  ***@gmail.com
    SMTP error from remote mail server after end of data:
    host gmail-smtp-in.l.google.com [2a00:1450:4010:c03::1a]:
    550-5.7.1 [2002:2e94:3a01:b:ea94:f6ff:fe07:5361      12] Our system has detected
    550-5.7.1 that this message is likely unsolicited mail. To reduce the amount of
    550-5.7.1 spam sent to Gmail, this message has been blocked. Please visit
    550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for
    550 5.7.1 more information. zl4si1280259lbb.125 - gsmtp

------ This is a copy of the message, including all the headers. ------

Return-path: <[email protected]***.ru>
Received: from c381558 by h5dns.net with local (Exim 4.80.1)
        (envelope-from <[email protected]***ru>)
        id 1Y0uZf-0007rI-1w
        for ***@gmail.com; Tue, 16 Dec 2014 20:02:11 +0400
To: NAME <***@gmail.com>
Subject: =?UTF-8?B?0KDQtdCz0LjRgdGC0YDQsNGG0LjRjw==?=
X-PHP-Originating-Script: 530:class.phpmailer.php
Date: Tue, 16 Dec 2014 20:02:11 +0400
From: =?UTF-8?B?0J/QvtGH0YLQvtCy0LjQuiBOZXdzVHJhdmVsbGVy?= <[email protected]***.ru>
Message-ID: <[email protected]***.ru>
X-Priority: 3
X-Mailer: PHPMailer 5.2.1 (http://code.google.com/a/apache-extras.org/p/phpmailer/)
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/html; charset="UTF-8"

Текст письма.

Who faced this problem, explain on the fingers what is the mistake?
PS If you send directly from the mailbox, through Yandex mail, then the messages reach you normally.

Answer 1

Start with the returned link support.google.com/mail/bin/answer.py?hl=en&answer... and following the Bulk Senders Guidelines

Answer 2

the use of spf/dkim significantly increases the likelihood that mail will not be recognized as spam
p.s.
I have my own mailserver, so I can set it up myself. how is it with Yandex, you need to find out