title: php mail function failed to send html email to hotmail and aol address
body: <p>I created a html newsletter and I want to use php mail() function to send the newsletter to customers email address in the user database. Before doing it, I test serval address that include gmail, hotmail, AOL, and yahoo. The gmail and yahoo instantly receive the html format email and everything works well(style and image displayed as designed), however the hotmail and AOL are not receive anything. I test sending a simple text email using mail() to hotmail and AOL, after waiting for long time (one night), they are able to receive the text format email. So I don't know what is wrong with hotmail and AOL. Is anyone having the same issue and knowing how to fix it?</p>
  
  <p>Here is my header setting </p>
  
  <pre><code>    $subject = 'News Letter';
  
      $headers = "From: sales@example.com\r\n";
      $headers .= "Reply-To: sales@example.com\r\n";
      $headers .= "Return-Path:sales@example.com\r\n";
      $headers .= "MIME-Version: 1.0\r\n";
      $headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";
  
  
  mail($email, $subject, $message, $headers); 
  </code></pre>