title: PHP mail causing phishing warning on gmail
body: <p>I am using PHPMailer to send automated e-mails from my website and while testing, I noticed that when I sent mail from website by Gmail, then e-mails sent by php mailer are generating the following warning on the recipients end:
  This message may not have been sent by: example@gmail.com Learn more Report phishing.
  But when I use other emails (like yahoo, outlook), then I got no emails in my <code>$contact_email</code>. Please help me to solve this problem. </p>
  
  <p>PHP Mailer code:</p>
  
  <pre class="lang-php prettyprint-override"><code>&lt;?php 
  global $_REQUEST;
  $response = array('error'=&gt;'');
  
      $user_name = substr($_REQUEST['user_name'], 0, 20);
      $user_email = substr($_REQUEST['user_email'], 0, 40);
      $user_msg = $_REQUEST['user_msg'];
  
      $contact_email = 'contact.arefin@gmail.com';    
  
      if (trim($contact_email)!='') {
          $subj = 'Message from Official Website';
          $msg = "Name: $user_name
          E-mail: $user_email
          Message: $user_msg";
  
          $head = "Content-Type: text/plain; charset=\"utf-8\"\n"
              . "X-Mailer: PHP/" . phpversion() . "\n"
              . "Reply-To: $user_email\n"
              . "To: $contact_email\n"
              . "From: $user_email\n";
  
          if (!@mail($contact_email, $subj, $msg, $head)) {
              $response['error'] = 'Error send message!';
          }
      } else 
              $response['error'] = 'Error send message!';
  
      echo json_encode($response);
      die();
  
  ?&gt;
  </code></pre>