Using Zoho mail, PHP mail() goes to spam.

Okay, I’m a very newbie to Linux servers.

I am running LAMP stack on my droplet. All the mail system is powered by Zoho mail (some kind like Google Apps).

I wrote a PHP web app, and the e-mail sent from mail() goes directly to spam in Gmail.

Here is the information obtained from Gmail when I send my Email from the PHP web app:

Delivered-To: t******@gmail.com
Received: by 10.202.168.206 with SMTP id r197csp2640062oie;
        Mon, 1 Feb 2016 01:03:13 -0800 (PST)
X-Received: by 10.107.131.155 with SMTP id n27mr4882881ioi.132.1454317393436;
        Mon, 01 Feb 2016 01:03:13 -0800 (PST)
Return-Path: <www-data@srakrn.com>
Received: from srakrn.com ([128.199.248.75])
        by mx.google.com with ESMTPS id u4si13948179igr.88.2016.02.01.01.03.12
        for <t******@gmail.com>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Mon, 01 Feb 2016 01:03:13 -0800 (PST)
Received-SPF: neutral (google.com: 128.199.248.75 is neither permitted nor denied by best guess record for domain of www-data@srakrn.com) client-ip=128.199.248.75;
Authentication-Results: mx.google.com;
       spf=neutral (google.com: 128.199.248.75 is neither permitted nor denied by best guess record for domain of www-data@srakrn.com) smtp.mailfrom=www-data@srakrn.com
Received: from srakrn.com (localhost [127.0.0.1])
by srakrn.com (8.14.4/8.14.4/Debian-4.1ubuntu1) with ESMTP id u1193BBg002012
	for <t******@gmail.com>; Mon, 1 Feb 2016 04:03:11 -0500
Received: (from www-data@localhost)
	by srakrn.com (8.14.4/8.14.4/Submit) id u1193B54002011;
	Mon, 1 Feb 2016 04:03:11 -0500

The line “Received: from srakrn.com (localhost [127.0.0.1])” made me think I’m configuring something very, very wrong.

I’ve tried changing the host name to srakrn.com, and tried editing /etc/hosts to make sure the IP points to my domain. What can I do next?