How to send email with attachements ?

Hello,

How to send email with attachments ?

I have write the following code in a submit form :
I received the mail but without the attachment...

 $values = $form_state['values']; //result from my form
  
  $mail_message = 'test';

  $module = 'my_module';
  $key = 'contact';

  $to = 'mail_to@mail.com';
  $from = 'mail_from@mail.com';

  $params = array(
    'subject' => 'Contact ' . transliteration_get($values['type']) . ' - ' . transliteration_get($values['subject']),
    'message' => $mail_message,
  );

//my attachment
  if(isset($values['file_1']) && $values['file_1'] != 0)
  {
    $file = file_load($values['file_1']); //form return fid, I load file for infos
    $file_content = file_get_contents(file_create_url($file->uri));

      $attachment = array(
         'filecontent' => $file_content,
         'filename' => $file->filename,
         'filemime' => $file->filemime,
       );
    $params['attachments'][] = $attachment;
  }

  $language = language_default();

  $send = TRUE;
  $result = drupal_mail($module, $key, $to, $language, $params, $from, $send);
  if ($result['result'] == TRUE) {
    drupal_set_message(t('Your message has been accepted'));
  }
  else {
    drupal_set_message(t('There was a problem sending your message and it was not sent.'), 'error');
  }

My code in my_module_mail (hook_mail) :

switch ($key) {
    case 'contact':
      $headers = array(
        'MIME-Version' => '1.0',
        'Content-Type' => 'text/html; charset=UTF-8;',
        'X-Mailer' => 'Drupal',
      );
      foreach ($headers as $key => $value) {
          $message['headers'][$key] = $value;
      }
      
      $message['subject'] = t($params['subject'], $options);
      $message['body'][] = $params['message'];

      $message['params']['attachments'] = $params['attachments'];

      break;
  }

Should we change the content type ? If I set "multipart/mixed", MailjetSmtpMailSystem asks a boundary...

Thanks for your help.