GMail不会标记电子邮件html（通过PHP发送）

// To send HTML mail, the Content-type header must be set
$headers  = \'MIME-Version: 1.0\' . \"\\r\\n\";
$headers .= \'Content-type: text/html; charset=iso-8859-1\' . \"\\r\\n\";

// Mail it
mail($to, $subject, $message, $headers);

<span style=\'font-style:italic;\'>Italic Text</span>

<em>Italic Text</em>