postfix - Mail marked as spam (Gmail/Hotmail): IP not on blacklist, DKIM Valid, SPF Valid and DMARC valid

I'm trying to send mail from my own domain (which is 15 days old now) but I'm having some troubles. Check the following mail body:

Delivered-To: ------@gmail.com
Received: by 10.25.89.200 with SMTP id n191csp1613325lfb;
        Mon, 15 Jun 2015 14:20:52 -0700 (PDT)
X-Received: by 10.194.157.194 with SMTP id wo2mr55865555wjb.103.1434403252309;
        Mon, 15 Jun 2015 14:20:52 -0700 (PDT)
Return-Path: <----@mydomain>
Received: from mymaildomain (mail.mymaildomain [])
        by mx.google.com with ESMTP id fj6si20368790wib.55.2015.06.15.14.20.52

        for <------@gmail.com>;
        Mon, 15 Jun 2015 14:20:52 -0700 (PDT)
Received-SPF: pass (google.com: domain of me@mydomain designates  as permitted sender) client-ip=;
Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of me@mydomai designates 149.210.155.34 as permitted sender) smtp.mail=me@mydomain;
       dkim=pass header.i=@mydomain;
       dmarc=pass (p=QUARANTINE dis=NONE) header.from=mydomain
Message-ID: <557F41B3.2080107@mydomain>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mydomain; s=mail;
    t=1434403152; bh=Wguxgu2qx/vIvpYIpENoa5tTcUlTNO8hTPP2ckEi6NY=;

    h=Date:From:To:Subject:From;
    b=UFG7EP9F9iFkBdra7TIfQ8q5iexmyT0Jt1Ay/aW+8Z4ti6/G/HPcVk1SIdmuR6RoH
     4LkkkKAnHhbae5pZz+oMMIXI3yeAI/n3EQnzdT5TmNBo3K7YluDmfA1yQ8pRL6VE51
     VGWdZh+hmimLfR+p1Lnu5BVrQmksURduB0yxlhM4=
Date: Mon, 15 Jun 2015 23:20:51 +0200
From: me@mydomain
To: ----@gmail.com
Subject: Test 20000
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit


Just a small test

As you can see the DKIM, SPF and DMARC are all passing in Gmail, but Gmail (and Hotmail) keep flagging my mails as spam. I Already followed the guides in https://support.google.com/mail/answer/1366858?hl=en-GB&expand=5 and https://mail.live.com/mail/junkemail.aspx but they offer no conclusive information. I also looked at various other Stackoverflow questions, but those all contained dead links for (human) support from Hotmail/Gmail.

The domain is a .EU domain and the IP comes from TransIP (Dutch VPS hoster). I even subscribed to the Junk Email Reporting program (JMRP) and the Smart Network Data Services program (SNDS) of Microsoft and added my contact info to abuse.net. But still no luck after checking it every day..

How can I resolve this issue? How can I contact Google/Hotmail about this problem, and why is my e-mail flagged as spam, it's fully authenticated and does not contain any "shady" content?

I contacted Hotmail about the spam issue and they did responded with the actions I already had taken. Gmail accepts my mail als legit if I send it over IPv6 (which I configured by default now). And no, my IP is not in a blacklist.