Emails from webserver going to spam folder

I have had an ongoing issue with emails sent from my vps server occasionally being rejected or sent to a spam folder. Hotmail/outlook.com is one of the email systems sending the emails to spam, so I created an outlook.com account to test with.

I have recently taken up this issue again because I just went through David Powers' good tutorial on swiftmailer at lynda.com. Using the swiftmailer class, I have created a new mail process. I have included the email header from the outlook.com email that was sent directly to the spam/junk folder. If anyone can see in it any clue as to why the email was sent to spam, I would appreciate it. First some notes:

• I replaced all the encrypted strings with [goobledygook]
• I replaced my domain names with domainname.net and otherdomain.net. My actual domain names are not on any email blacklist. I also replaced my ip address
• Note that spf = pass and dkim = pass
• The from address is on the same domain as the vps server but the form that processed the email is on a different domain (same server) otherdomain.net

Thanks for any thoughts. Headers follow:

x-store-info:[goobledygook]
Authentication-Results: hotmail.com; spf=pass (sender IP is 01.01.01.01) smtp.mailfrom=rhecker@domainname.net; dkim=pass header.d=domainname.net; x-hmca=pass header.id=rhecker@domainname.net
X-SID-PRA: rhecker@domainname.net
X-AUTH-Result: PASS
X-SID-Result: PASS
X-Message-Status: n:n
X-Message-Delivery: [goobledygook]
X-Message-Info: [goobledygook]=
Received: from vps.domainname.net ([01.01.01.01]) by COL004-MC2F47.hotmail.com over TLS secured channel with Microsoft SMTPSVC(7.5.7601.23143);
     Sat, 5 Mar 2016 07:01:43 -0800
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
    d=domainname.net; s=default; h=Content-Transfer-Encoding:Content-Type:
    MIME-Version:To:Reply-To:From:Subject:Date:Message-ID;
    bh=[four lines of gobbledygook]==;
Received: from vps.domainname.net ([01.01.01.01]:37348 helo=otherdomain.net)
    by vps.domainname.net with esmtpa (Exim 4.86_1)
    (envelope-from <rhecker@domainname.net>)
    id 1acDiA-0000uv-R8
    for domainname@outlook.com; Sat, 05 Mar 2016 07:01:42 -0800
Message-ID: <[gobbledygook]@otherdomain.net>
Date: Sat, 05 Mar 2016 07:01:42 -0800
Subject: Website Message from Roger Right
From:  - No Reply <rhecker@domainname.net>
Reply-To: rob@robhecker.com
To: domainname@outlook.com
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - vps.domainname.net
X-AntiAbuse: Original Domain - outlook.com
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain - domainname.net
X-Get-Message-Sender-Via: vps.domainname.net: authenticated_id: rhecker/from_h
X-Authenticated-Sender: vps.domainname.net: rhecker@domainname.net
X-Source:
X-Source-Args:
X-Source-Dir:
Return-Path: rhecker@domainname.net
X-OriginalArrivalTime: 05 Mar 2016 15:01:43.0638 (UTC) FILETIME=[EE383F60:01D176EF]

This is the second try. Hope it gets there.