title: Mail not getting send to specific domains
body: <p>We have a VPS with CentOS combined with DirectAdmin which we use for a Magento shop. This runs fine, except for sending email.</p>
  
  <p><strong>Problem:</strong><br>
  It appears that some specific domains won't receive our emails and we get a bounce. If we use any other email sending systems, the mails arrive without problems.</p>
  
  <p>The bounce mail contains the following error:</p>
  
  <blockquote>
    <p>SMTP error from remote mail server after HELO Company-Shops:<br>
    host mx-cluster-b2.one.com [<em>IP ADRESS</em>]: 504 5.5.2 :
    Helo command rejected: need fully-qualified hostname</p>
  </blockquote>
  
  <p>After googling and trying things for a week now, I am a bit lost. I tried checking postfix in CentOS, but this is not installed and I'm not quite sure if this is needed.</p>
  
  <p><strong>Possible issue?</strong><br>
  I believe the hostfile in CentOS is setup incorrectly:</p>
  
  <blockquote>
    <p>127.0.0.1 localhost localhost.localdomain localhost4 ... etc<br>
    <em>OUR IP</em> Company-Shops</p>
  </blockquote>
  
  <p>'Company-Shops' should probably be a domain name, am I right? The same as the rDNS. But I'm afraid if I change this it will kill my site and whatnot. I'm not sure if this entry correlates with the 'company-Shops' helo label in the bounce error.</p>
  
  <p><strong>Some extra info:</strong><br>
  - We use the webmail Roundcube from DirectAdmin<br>
  - At the moment we run one shop, but this might grow a bit (multiple sites on 1 IP)<br>
  - We don't use subdomains <br>
  - We've set up a reverse DNS, with the domain</p>
  
  <p>Is there anyone with similiar experiences or with a bit more knowledge about this subject? I appreciate any advice we can get, as we are stuck.. </p>
  
  <p>Many thanks.</p>