PHP mail with attachment of unknown file type

Question

I want to add send mail in my website. user can attach some files with multiple types in email. So i wrote this code to send mail. the problem is file type is not correct. for example i attached a jpg file to send to email. but the attachment received in mail box is empty or is wrong type. this is my php mail file:

<?php

    //Deal with the email
    $sender = $_POST['email'];

    $to = 'info@matinjewellery.com';
    $subject = $_POST['name'];

    $message = strip_tags($_POST['message']);
    $attachment = chunk_split(base64_encode(file_get_contents($_FILES['file']['tmp_name'])));
    $filename = $_FILES['file']['name'];

    $boundary =md5(date('r', time())); 

    $headers = "From: ".$sender."\r\nReply-To: ".$to;
    $headers .= "\r\nMIME-Version: 1.0\r\nContent-Type: multipart/mixed; boundary=\"_1_$boundary\"";

    $message="This is a multi-part message in MIME format.

 --_1_$boundary
Content-Type: multipart/alternative; boundary=\"_2_$boundary\"

 --_2_$boundary
 Content-Type: text/plain; charset=\"utf-8\"
 Content-Transfer-Encoding: 7bit

 $message

 --_2_$boundary--
 --_1_$boundary
 Content-Type: application/zip; name=\"$filename\" 
 Content-Transfer-Encoding: base64 
 Content-Disposition: attachment 
 $attachment
 --_1_$boundary--";
mail($to, $subject, $message, $headers);    
?>