Mail land in Google's spam box

Hello,

When I send mail from Roundcube (or Thunderbird) they land in Google's spam box.

Here is the message's source:
Delivered-To: receiver@gmail.com
Received: by 10.202.66.194 with SMTP id p185csp132269oia;
        Tue, 24 Jun 2014 02:20:10 -0700 (PDT)
X-Received: by 10.180.90.242 with SMTP id bz18mr33049880wib.12.1403601609800;
        Tue, 24 Jun 2014 02:20:09 -0700 (PDT)
Return-Path: <sender@publicitem.pro>
Received: from mail.publicitem.fr (mail.publicitem.fr. [62.210.76.93])
        by mx.google.com with ESMTPS id s1si20619018wiw.15.2014.06.24.02.20.06
        for <receiver@gmail.com>
        (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Tue, 24 Jun 2014 02:20:07 -0700 (PDT)
Received-SPF: pass (google.com: domain of sender@publicitem.pro designates 62.210.76.93 as permitted sender) client-ip=62.210.76.93;
Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of sender@publicitem.pro designates 62.210.76.93 as permitted sender) smtp.mail=sender@publicitem.pro;
       dkim=pass header.i=@publicitem.pro
Received: from localhost (localhost.localdomain [127.0.0.1])
    by mail.publicitem.fr (Postfix) with ESMTP id 4F083138036A
    for <receiver@gmail.com>; Tue, 24 Jun 2014 11:20:04 +0200 (CEST)
Authentication-Results: mail.publicitem.fr (amavisd-new);
    dkim=pass (1024-bit key) reason="pass (just generated, assumed good)"
    header.d=publicitem.pro
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=publicitem.pro;
     h=user-agent:message-id:subject:subject:to:from:from:date:date
    :content-transfer-encoding:content-type:content-type
    :mime-version; s=dkim; t=1403601603; x=1404465604; bh=g9+eoSPPPF
    0ze7iUIO5Wvo0w0mhmixl30HZywt3Qj4I=; b=DVJCpeDeouci2FhCLxJWhSe1ZL
    yfo2Qzwd3KU/Tyg88U1aHXOQ0OJdqXSwqPXzRQJhybkH2K37wdJJs3Nc5KG5Zyzz
    xpShZrIAgnqN6gevTLgGO/dtfGCEMTWQNsZ6qs2d1+eOjS94nK65ppMsz+L/RPud
    WUutgm0/TifSqBgN8=
X-Virus-Scanned: Debian amavisd-new at mail.publicitem.fr
Received: from mail.publicitem.fr ([127.0.0.1])
    by localhost (mail.publicitem.fr [127.0.0.1]) (amavisd-new, port 10024)
    with ESMTP id eghOD5LTMOOo for <receiver@gmail.com>;
    Tue, 24 Jun 2014 11:20:03 +0200 (CEST)
Received: from www.publicitem.pro (localhost.localdomain [127.0.0.1])
    by mail.publicitem.fr (Postfix) with ESMTPSA id BCE6B1380E66
    for <receiver@gmail.com>; Tue, 24 Jun 2014 11:20:02 +0200 (CEST)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
format=flowed
Content-Transfer-Encoding: 8bit
Date: Tue, 24 Jun 2014 11:20:02 +0200
From: sender@publicitem.pro
To: receiver@gmail.com
Subject: Fuite
Return-Receipt-To: sender@publicitem.pro
Disposition-Notification-To: sender@publicitem.pro
Message-ID: <ad43a070917a5add8205aed36a6b1a1a@publicitem.pro>
X-Sender: sender@publicitem.pro
User-Agent: Roundcube Webmail
X-Antivirus: avast! (VPS 140623-1, 23/06/2014), Inbound message
X-Antivirus-Status: Clean

Et Je me suis enfui
Je suis devenu Sphinx
Et mille ans sont passés
au doux son de Syrinx

Et Je me suis enfui
J’ai acosté à Tyr
Et quand le soleil fût
je ressortis ma Lyre

Et je me suis enfui
Et coupait au silex
Je m’enivrai la nuit
des horizons convexes

Et je me suis enfui
Pour ne jamais revoir
l’Aube

What is wrong in my configuration? Thx for any help.

==== Required information ====
- iRedMail version: iRedMail-0.8.7
- Store mail accounts in which backend : MySQL
- Linux/BSD distribution name and version: Ubuntu LTS 14.04 64 bits
- Related log if you're reporting an issue:
====