function is_email_address_unsafe( $user_email ) {
  $banned_names = get_site_option( 'banned_email_domains' );
  if ( $banned_names && ! is_array( $banned_names ) ) {
    $banned_names = explode( "\n", $banned_names );
  }

  $is_email_address_unsafe = false;

  if ( $banned_names && is_array( $banned_names ) && false !== strpos( $user_email, '@', 1 ) ) {
    $banned_names     = array_map( 'strtolower', $banned_names );
    $normalized_email = strtolower( $user_email );

    list( $email_local_part, $email_domain ) = explode( '@', $normalized_email );

    foreach ( $banned_names as $banned_domain ) {
      if ( ! $banned_domain ) {
        continue;
      }

      if ( $email_domain == $banned_domain ) {
        $is_email_address_unsafe = true;
        break;
      }

      $dotted_domain = ".$banned_domain";
      if ( $dotted_domain === substr( $normalized_email, -strlen( $dotted_domain ) ) ) {
        $is_email_address_unsafe = true;
        break;
      }
    }
  }

  
/**
 * Filters whether an email address is unsafe.
 *
 * @since 3.5.0
 *
 * @param bool   $is_email_address_unsafe Whether the email address is "unsafe". Default false.
 * @param string $user_email              User email address.
 */
  return apply_filters( 'is_email_address_unsafe', $is_email_address_unsafe, $user_email );
}