Unable to send email with file attachment that is submitted via a PHP form

Question

edit: this question is different as i am specifically asking about the attachment feature not working in my code otherwise y php and html code run fine.

I have tried to create a submission form which attaches a file of any type and sends it through to my email. Unfortunately, it doesn't deliver to my email address.

here is my PHP & HTML code(I have removed my email address purposely):

<?php if (isset($_POST)) {
  //form validation vars
  $formok=true;
  $errors=array();

  $ipaddress=$_SERVER['REMOTE_ADDR'];
  $date=date('d/m/Y');
  $time=date('H:i:s');

  $name=$_POST['name'];
  $email=$_POST['email'];
  $telephone=$_POST['telephone'];
  $message=strip_tags($_POST['message']);
  $attachment=chunk_split(base64_encode(file_get_contents($_FILES['file']['tmp_name'])));
  $filename=$_FILES['file']['name'];
  $boundary=md5(date('r', time()));

  if (empty($name)) {
    $formok=false;
    $errors[]="You have not entered a name";
  }

  if (empty($email)) {
    $formok=false;
    $errors[]="You have not entered an email address";
  }
  elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $formok=false;
    $errors[]="You have not entered a valid email address";
  }

  if ($formok) {
    $headers="From: " . $email ."\r\n";
    $headers .="\r\nMIME-Version: 1.0\r\nContent-Type: multipart/mixed; boundary=\"_1_$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=\"iso-8859-1\"
Content-Transfer-Encoding: 7bit
 $message --_2_$boundary-- --_1_$boundary Content-Type: application/octet-stream;
    name=\"$filename\" 
Content-Transfer-Encoding: base64 Content-Disposition: attachment $attachment --_1_$boundary--";
 mail("fdgfdg@gfdg.com ", "New Submission", $emailbody, $headers);
  }
  if ($formok) {
    $headers="From: gfdg@gfd.com" ."\r\n";
    $headers .='Content-type: text/html; charset=iso-8859-1' ."\r\n";
    $emailbody="<p>We have recieved your submission and will be in contact with you shortly.";
    mail($email, "Thank You", $emailbody, $headers);
  }
  //what we need to return back to our form
  $returndata=array('posted_form_data'=> array('name'=> $name,
  'email'=> $email,
  'telephone'=> $telephone,
  'file'=> $attachment,
  'message'=> $message),
  'form_ok'=> $formok,
  'errors'=> $errors);
  //if this is not an ajax request
  if (empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) !=='xmlhttprequest') {
    //set session variables
    session_start();
    $_SESSION['cf_returndata']=$returndata;
    //redirect back to form
    header('location: ' . $_SERVER['HTTP_REFERER']);
  }
}

<form enctype="multipart/form-data" method="post" action="processsubmit.php">
  <label for="name">Name: <span class="required">*</span>
  </label>
  <input type="text" id="name" name="name" value="" placeholder="John Doe" required="required" autofocus="autofocus" />

  <label for="email">Email Address: <span class="required">*</span>
  </label>
  <input type="email" id="email" name="email" value="" placeholder="johndoe@example.com" required="required" />

  <label for="telephone">Telephone:</label>
  <input type="tel" id="telephone" name="telephone" value="" />

  <label for="file">File</label>
  <input type="file" name="file" id="file">


  <label for="message">Message: <span class="required">*</span>
  </label>
  <textarea id="message" name="message" placeholder="Your message must be greater than 20 charcters" required="required" data-minlength="20"></textarea>

  <span id="loading"></span>
  <input type="submit" value="Holla!" id="submit-button" />
  <p id="req-field-desc"><span class="required">*</span> indicates a required field</p>
</form>