Use dkim in phpmailer code with privacy key - phpmailer

Question

I am using PHPMailer.
I added DKIM attributes when sending file.
The code is like:
// $mail is PHPMailer class
$mail->SMTPAuth = true;
$mail->SMTPSecure = "ssl";
$mail->Host = "*******";
$mail->Port = ***;
$mail->Mailer= "SMTP";
//...
$mail->DKIM_domain = 'mydomain.com';
$mail->DKIM_identity = '#mydomain.com';
$mail->DKIM_private = __DIR__ . '/privacy_key_mydomain.txt';
$mail->DKIM_selector = 'default';
$mail->DKIM_passphrase = ''; // only ssl.
//...
(Same as example on: Send mail in phpmailer using DKIM Keys)
When sending to email, such as mine (gmail), I have no problem, and I see that my email is signed by mydomain.com.
I see also, in the email source that DKIM-Signature is sent.
Nevertheless, some of my clients I am sending emails reject my email, with following message (especially for yahoo emails - more that 90% of rejects uses yahoo for their emails).
554 Message not allowed - Headers are not RFC compliant[291]
As I did some workaround, I found this message to be detected as a spam.
I am using CPANEL for my site, which has round-cube - so I test it at round-cube (sending the customer a message with round-cube) - seems OK. No spam detect.
So, I suspect the privacy key file may be incorrect (I have an SSL site - so I use the same privacy key as my own site).
What may be wrong? What shall I check out in order to avoid my emails will be detected as spams?
Here is the email source result:
Delivered-To: myaccount#gmail.com
Received: by 10.114.75.12 with SMTP id y12csp118366ldv;
Tue, 15 Jul 2014 11:44:11 -0700 (PDT)
X-Received: by 10.140.104.49 with SMTP id z46mr36090427qge.74.1405449850437;
Tue, 15 Jul 2014 11:44:10 -0700 (PDT)
Return-Path: <support#mydomain.com>
Received: from lin9.maindomain10.net (lin9.maindomain10.net. [1.2.3.4])
by mx.google.com with ESMTPS id t14si21957304qac.66.2014.07.15.11.44.09
for <myaccount#gmail.com>
(version=TLSv1 cipher=RC4-SHA bits=128/128);
Tue, 15 Jul 2014 11:44:10 -0700 (PDT)
Received-SPF: pass (google.com: domain of support#mydomain.com designates 1.2.3.4 as permitted sender) client-ip=1.2.3.4;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of support#mydomain.com designates 1.2.3.4 as permitted sender) smtp.mail=support#mydomain.com;
dkim=pass header.i=#mydomain.com
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mydomain.com; s=default;
h=Content-Type:Content-Transfer-Encoding:MIME-Version:Message-ID:Subject:Reply-To:From:To:Date:Subject:To; bh=HBLjhR1eb0w5FQ9aVj60Gu0x3jP9XWQ7LQkpzTRHjfQ=;
b=ECWMCs3iPsjuvlT473K9u3skwyNRVunmnv3p440Nk2ZJVrbuWoO0vgzaWM8gjCC503ADKivdfrrOek8TgTSEI7G4B3WMCHI50PWq68W5rcscYJqErWxuqAVcSl4r5tomk88AYPhHiotCugmRTjwQ2K/JBtHsAvMhTlVQMMXsMl0=;
Received: from mainuser by lin9.maindomain10.net with local (Exim 4.82)
(envelope-from <support#mydomain.com>)
id 1X77hp-0001f9-SH; Tue, 15 Jul 2014 14:44:01 -0400
To: myName Mizrahi <myaccount#gmail.com>
Subject: Statistics from Sample Name site
Date: Tue, 15 Jul 2014 14:44:01 -0400
To: myName Mizrahi <myaccount#gmail.com>
From: "donotreply#mydomain.com" <root#localhost>
Reply-To: Sample Name site <donotreply#mydomain.com>
Subject: Statistics from Sample Name site
Message-ID: <d984a2c6308ef2a97cf6ccfe6292263a#mydomain.com>
X-Priority: 3
X-Mailer: PHPMailer 5.2.4 (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
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - lin9.maindomain10.net
X-AntiAbuse: Original Domain - gmail.com
X-AntiAbuse: Originator/Caller UID/GID - [927 895] / [47 12]
X-AntiAbuse: Sender Address Domain - mydomain.com
X-Get-Message-Sender-Via: lin9.maindomain10.net: authenticated_id: mainuser/sender_address_domain
When sending message from round-cube, the email source look like this:
Delivered-To: myaccount#gmail.com
Received: by 10.114.75.12 with SMTP id y12csp118605ldv;
Tue, 15 Jul 2014 11:48:53 -0700 (PDT)
X-Received: by 10.224.161.129 with SMTP id r1mr34110372qax.86.1405450132678;
Tue, 15 Jul 2014 11:48:52 -0700 (PDT)
Return-Path: <support#mydomain.com>
Received: from lin9.maindomain10.net (lin9.maindomain10.net. [1.2.3.4])
by mx.google.com with ESMTPS id x8si13226659qas.81.2014.07.15.11.48.52
for <myaccount#gmail.com>
(version=TLSv1 cipher=RC4-SHA bits=128/128);
Tue, 15 Jul 2014 11:48:52 -0700 (PDT)
Received-SPF: pass (google.com: domain of support#mydomain.com designates 1.2.3.4 as permitted sender) client-ip=1.2.3.4;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of support#mydomain.com designates 1.2.3.4 as permitted sender) smtp.mail=support#mydomain.com;
dkim=pass header.i=#mydomain.com
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mydomain.com; s=default;
h=Message-ID:Subject:To:From:Date:Content-Transfer-Encoding:Content-Type:MIME-Version; bh=Bynm51C7RZD/vZ81iEMKjxxLoAJtSmKFcwU/eyFzPs8=;
b=fUX+UKS9Ua0HK35AOBRBJbmqTEuKscCYAsPyxs3If3dhhvb/AvAjl1gR9Rz9AN0EX0mu275wtaN5Y1JWP+8w8VcGebJ9FEWsltCl9nwqL6bos/eEqJxTWjDG6ch9MHo3G0mSE326Pyc13JWa59InSgJyWi8MSstT1POfuEhfe28=;
Received: from localhost.localdomain ([127.0.0.1]:54911 helo=mydomain.com)
by lin9.maindomain10.net with esmtpa (Exim 4.82)
(envelope-from <support#mydomain.com>)
id 1X77mO-0001l7-1O
for myaccount#gmail.com; Tue, 15 Jul 2014 14:48:44 -0400
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
format=flowed
Content-Transfer-Encoding: 7bit
Date: Tue, 15 Jul 2014 14:48:43 -0400
From: support#mydomain.com
To: myaccount#gmail.com
Subject: test
Message-ID: <ed6307c2c9504e8ba9ec21f073d5f863#mydomain.com>
X-Sender: support#mydomain.com
User-Agent: Roundcube Webmail/0.9.5
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - lin9.maindomain10.net
X-AntiAbuse: Original Domain - gmail.com
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain - mydomain.com
X-Get-Message-Sender-Via: lin9.maindomain10.net: authenticated_id: support#mydomain.com
Round-Cube works with no spam.
What is the main difference that's make the issue?
Thanks :)

Answer 1

5.2.4 is pretty old and buggy - You need to update to the latest PHPMailer from GitHub.