PHP を使用して複数の添付ファイルを電子メールで送信するにはどうすればよいですか?

<code class="php">if ($_POST) {
    // Get the file names
    $files = $_FILES['csv_file']['name'];

    // Email fields
    $to = "[email protected]";
    $from = "[email protected]"; 
    $subject = "My subject"; 
    $message = "My message";
    $headers = "From: $from";

    // Boundary
    $semi_rand = md5(time()); 
    $mime_boundary = "==Multipart_Boundary_x{$semi_rand}x"; 

    // Headers for attachment 
    $headers .= "\nMIME-Version: 1.0\n" . "Content-Type: multipart/mixed;\n" . " boundary=\"{$mime_boundary}\""; 

    // Multipart boundary 
    $message = "This is a multi-part message in MIME format.\n\n" . "--{$mime_boundary}\n" . "Content-Type: text/plain; charset=\"iso-8859-1\"\n" . "Content-Transfer-Encoding: 7bit\n\n" . $message . "\n\n"; 
    $message .= "--{$mime_boundary}\n";

    // Preparing attachments
    foreach ($files as $file) {
        $file_data = file_get_contents($file);
        $file_data = chunk_split(base64_encode($file_data));
        $message .= "Content-Type: {\"application/octet-stream\"};\n" . " name=\"$file\"\n" . 
        "Content-Disposition: attachment;\n" . " filename=\"$file\"\n" . 
        "Content-Transfer-Encoding: base64\n\n" . $file_data . "\n\n";
        $message .= "--{$mime_boundary}\n";
    }

    // Send the email
    $ok = @mail($to, $subject, $message, $headers);
    if ($ok) { 
        echo "<p>mail sent to $to!</p>"; 
    } else { 
        echo "<p>mail could not be sent!</p>"; 
    }
}
?></code>

<code class="html"><form action="#" method="POST" enctype="multipart/form-data">
    <input type="file" name="csv_file[]" /><br/>
    <input type="file" name="csv_file[]" /><br/>
    <input type="file" name="csv_file[]" /><br/>
    <input type="submit" name="upload" value="Upload" /><br/>
</form></code>