How to send multiple files as attachments in an email using PHP?

<code class="php"><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>

<?php

if($_POST) {
    // Create arrays for file information
    $ftype = $_FILES['csv_file']['type'];
    $fname = $_FILES['csv_file']['name'];

    // Define files to be attached
    $files = $fname;

    // Email fields
    $to = "recipient@example.com";
    $from = "sender@example.com";
    $subject = "Attachments";
    $message = "Email with attached files";
    $headers = "From: $from";

    // Set MIME boundary
    $semi_rand = md5(time());
    $mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";

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

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

    // Prepare each attachment
    foreach ($files as $key => $value) {
        $file = fopen($value, "rb");
        $data = fread($file, filesize($value));
        fclose($file);
        $data = chunk_split(base64_encode($data));
        $message .= "Content-Type: {\"application/octet-stream\"};\n" . " name=\"$fname[$key]\"\n" .
        "Content-Disposition: attachment;\n" . " filename=\"$fname[$key]\"\n" .
        "Content-Transfer-Encoding: base64\n\n" . $data . "\n\n";
        $message .= "--{$mime_boundary}\n";
    }

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

?></code>