Why do emails sent by PHP script end up in spam?

Question

Domain Name System

Hello.
I've started work on the bulletin board, currently setting up mail. We will send three channels, from the server - all techno mail (confirmations, notifications and other garbage); with unisender - mailing list for groups from 500 souls; mail.ru - mail for personal communication, support and small groups.
DNS seems to be set up, but letters sent by the script end up in spam at yandex.

Received: from mxfront8g.mail.yandex.net ([127.0.0.1])
by mxfront8g.mail.yandex.net with LMTP id DFaSiffp
for ; Thu, 29 Oct 2015 19:05:58 +0300
Received: from unknown (unknown [46.101.179.4])
by mxfront8g.mail.yandex.net (nwsmtp/Yandex) with ESMTP id yiw1YapQmS-5vr4GwfM;
Thu, 29 Oct 2015 19:05:57 +0300
X-Yandex-Front: mxfront8g.mail.yandex.net
X-Yandex-TimeMark: 1446134757
Authentication-Results: mxfront8g.mail.yandex.net; spf=pass (mxfront8g.mail.yandex.net: domain of slap.com.ua designates 46.101.179.4 as permitted sender) [email protected]
X-Yandex-Spam: 4
Received: by do. localdomain (Postfix, from userid 998)
id D180440F6C; Thu, 29 Oct 2015 11:59:50 -0400 (EDT)
to : [email protected]
_ Thu, 29 Oct 2015 17:59:50 +0200 From: " slap.com.ua " < [email protected] > Message-ID: <[email protected]> X-Priority: 3 MIME- Version: 1.0 Content-Type: multipart/alternative; boundary="b1_7ebe218a9a47799aa0371a8105b4b61f" Content - Transfer-Encoding: 8bit Return-Path: [email protected]

Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Tell me what to do?

Answer 1

Before starting mailing, test through the mail-tester.com service,
it will also give a good report on problems.

Answer 2

Yandex requirements for honest mailings:
https://yandex.ru/support/mail/spam/honest-mailers.xml

Answer 3

Use ready-made mailing services, such as Unisender. They themselves make sure that the letter is delivered to the addressee.