Waarom kan laag streepje niet ?

<?php
ini_set(display_errors, 1);
error_reporting(E_ALL);


include "db_settings.php";
include "messaging.php";


if($_SERVER['REQUEST_METHOD'])
{
    $email = strtolower(trim($_POST['email']));


    if(!empty($_POST['email']))
    {
        if(eregi("^[0-9a-z]([-_.]?[0-9a-z])*@[0-9a-z]([-.]?[0-9a-z])*.[a-z]{2,4}$", $email))
        {
            $html = $_POST['html'];
            $email_host = explode("@", $email);
            $email_host = $email_host[1];
            $email_resolved = gethostbyname($email_host);


            if($email_resolved == $email_host)
            {
                echo $error8;
            } else
            {
                mysql_connect($hostname, $user, $password) or die($error3);
                mysql_select_db($db) or die($error4);


                $sql = "INSERT INTO newsletter (id_col,email,recieve,html) VALUES ('','" . $email . "','1','" . $html . "')";
                $res = mysql_query($sql);


                if(mysql_errno() == 1062)
                {
                    echo $error9;
                } else
                    if(!$res)
                    {
                        echo $error10;
                    } else
                    {
                        $to = $email;
                        $subject = $message2;
                        $headers = $message3;
                        $message = $message4;
                        mail($to, $subject, $message, $headers) or die($error11);


                        echo $message5;
                    }
            }


        } else
        {
            echo $error8;
        }
    } else
    {
        die($error12);
    }
}