Contact form 7 custom Validation

In my case I will add a custom validation on my subscriber email field to check if the email was already on the database.

This is my sample code below:

add_filter( 'wpcf7_validate_email*', 'hdev_custom_email_subscription_validation_filter', 20, 2 ); 
function hdev_custom_email_subscription_validation_filter( $result, $tag ) {
  if ( 'your-email-subscriber' == $tag->name ) { //tag name
    $your_email_subscriber = isset( $_POST['your-email-subscriber'] ) ? trim( $_POST['your-email-subscriber'] ) : ''; 
    global $wpdb;
    //check if the current email inputted is on the database
    $get_results = $wpdb->get_results("SELECT * FROM `wp_postmeta` 
    tbl1 LEFT JOIN `wp_postmeta` tbl2 ON tbl1.post_id=tbl2.post_id 
    WHERE (tbl1.meta_key = 'form_id' AND tbl1.meta_value = 863 ) 
    AND (tbl2.meta_key = 'wpcf7s_posted-your-email-subscriber' 
    AND tbl2.meta_value = '".$your_email_subscriber."')");
    if(!empty($get_results)){
      $result->invalidate( $tag, "This email address has been already subscribed!" );
    }
  }
  return $result;
}