Dkim = softfail with mail () but not with phpmailer?

I have a server that is running mail software. This software uses phpmailer. If I send an email through this software, I have no problem, I receive SPF=PASS

as well DKIM=PASS

.

However, when I try to use a regular PHP file that it just uses mail()

, I get an error dkim=softfail (fail, body has been altered) header.i=@example.com

. Below are the features.

I checked online for a couple of hours, but all I found was a link to the RFC specifications, stating that this issue was caused by things like "Lines over 990 bytes long" or "Final line endings" (both of which do not apply here as I am using chunk_split()

).

What could be causing this DKIM problem in my code? Is there another RFC specification that I am missing?

**PHP  I use:**

//build array with headers
$header = array();
$boundary = md5(uniqid(rand()));
$header[] = "MIME-Version: 1.0";
$header[] = "Content-Type: multipart/alternative; boundary = $boundary";
$header[] = "From: Me <me@example.com>";

// get html version
ob_start();
include('html.php');
$Html = ob_get_contents();
ob_end_clean();

// get TXT version
ob_start();
include('txt.php');
$Txt = ob_get_contents();
ob_end_clean();

// Build final message body
// TXT part of message
$body = "--$boundary\r\nContent-Type: text/plain; charset=UTF-8\r\nContent-Transfer-Encoding: base64\r\n";
$body .= chunk_split(base64_encode($Txt));

// HTML part of message
$body .= "--$boundary\r\nContent-Type: text/html; charset=UTF-8\r\nContent-Transfer-Encoding: base64\r\n";
$body .= chunk_split(base64_encode($Html));
$body .= "--$boundary--";

// sent email
$isMailed = mail("me@example.com","=?UTF-8?B?".base64_encode($subject)."?=",$body, implode("\n", $header));

      

        
        
        
      

    

EDIT: To help solve this problem, here is an example of an email header I receive with the above script:

Return-Path: <apache@example.com>
Delivered-To: me@example.com
Received: from localhost (mx1.example.com [127.0.0.1])
    by mx1.example.com (Postfix) with ESMTP id 4E50FBF31F
    for <me@example.com>; Tue, 16 Dec 2014 16:54:43 +0100 (CET)
X-Virus-Scanned: Debian amavisd-new at mx1.example.com
Authentication-Results: mx1.example.com (amavisd-new);
    dkim=softfail (fail, body has been altered) header.i=@example.com
Received: from mx1.example.com ([127.0.0.1])
    by localhost (mx1.example.com [127.0.0.1]) (amavisd-new, port 10024)
    with ESMTP id o8MXZhIlf1tF for <me@example.com>;
    Tue, 16 Dec 2014 16:54:42 +0100 (CET)
Received: from example.com (example.com [123.23.45.67])
    by mx1.example.com (Postfix) with SMTP id 92A21AF218
    for <me@example.com>; Tue, 16 Dec 2014 16:54:41 +0100 (CET)
Received: from localhost (mailsvr [127.0.0.1])
    by example.com (Postfix) with ESMTP id 895B51018227
    for <me@example.com>; Tue, 16 Dec 2014 16:56:23 +0100 (CET)
X-Virus-Scanned: amavisd-new at example.com
Received: from example.com ([127.0.0.1])
    by localhost (mailsvr.example.com [127.0.0.1]) (amavisd-new, port 10024)
    with LMTP id gm+3YJEGgEc7 for <me@example.com>;
    Tue, 16 Dec 2014 16:56:22 +0100 (CET)
Received: by example.com (Postfix, from userid 47)
    id A973B317802E; Tue, 16 Dec 2014 16:56:20 +0100 (CET)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=example.com;
    s=default; t=1418745380;
    bh=wL3reSbwXm4SPw5A8n9RooRKg+7j0rkM5+iBCFG51XI=;
    h=To:Subject:MIME-Version:Content-Type:From:Message-Id:Date;
    b=BALRnjP3rx8LcYUxvrLBSASiZyFgA5ckTvGHoKF4V+o8JOLtLTmpmPQS91ohHIwOq
     UFRhv6qJl9ObvFWl0c6QyVthGjCz2+2vB6RkMXQxzJgwxPIe6X51iIEDxA4Y3EYs+x
     0DxmjMTt5tNKNBrjvEtZiEolkfbua8cearxA/Q3M=
To: me@example.com
Subject: =?UTF-8?B?dGVzdA==?=
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary = 47eacbbcbff31a13d0894e4f9ac0450b
From: Me <me@example.com>
Message-Id: <20141216155620.A972B387802D@example.com>
Date: Tue, 16 Dec 2014 16:56:20 +0100 (CET)

--47eacbbcbff31a13d0894e4f9ac0450b
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: base64

dGVzdA==
--47eacbbcbff31a13d0894e4f9ac0450b
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: base64

PGh0bWw+PGhlYWQ+PC9oZWFkPg0KPGJvZHk+DQo8cD50ZXN0PC9wPg0KPC9ib2R5Pg0KPC9odG1s
Pg==
--47eacbbcbff31a13d0894e4f9ac0450b--