Please implement this code in your scripts, and deny registering to users if $error is filled. Replace $usk_email with your own data.

$error = '';
$usk_provider = 'http://uspam.pagerobot.com/index.php?email=%s&ip=%s';
$usk_error = 0;
$usk_email = ' Questo indirizzo e-mail è protetto dallo spam bot. Abilita Javascript per vederlo. ';
$usk_query = sprintf($usk_provider, $usk_email, $_SERVER['REMOTE_ADDR']);
$usk_result = 0;

$fp = 0;
if(function_exists('curl_init') && $fp = curl_init())
{
    // Use CURL
    curl_setopt($fp, CURLOPT_CONNECTTIMEOUT, 10);
    curl_setopt($fp, CURLOPT_TIMEOUT, 30);
    curl_setopt($fp, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($fp, CURLOPT_FAILONERROR, 1);
    curl_setopt($fp, CURLOPT_URL, $usk_query);
    $curl_result = curl_exec($fp);
    if(!$usk_error = curl_errno($fp))
    {
        // Connection established successfully
        $usk_result = intval($curl_result);
    }
    curl_close($fp);
}

if(!$fp && $fp = @fopen($usk_query, 'r'))
{
    // Use standard connection
    $usk_result = intval(@fread($fp, 16));
    @fclose($fp);
}

if(!$fp && !$usk_error)
{
    // Assign default error if there was no read and no error
    $usk_error = -1;
}

if(!$usk_error)
{
    switch($usk_result)
    {
        case 0:
            // Invalid email address
            $error = 'Invalid email address';
            break;
        case 1:
            // Valid email address, do nothing
            break;
        default:
            // Site manually down
            $usk_error = -1;
    }
}