Drupal 7, Disable mail sending if condition is right.

lb_registration.module

/**
 * Implements hook_mail_alter().
 */
function MYMODULE_mail_alter(&$message) {
  if ($message['key'] == 'register_confirmation_with_pass') {
    $user = $message['params']['account'];

    // If user account need to approve we ignore standard mail after registration
    // because we have custom mails for this case.
    if (lb_registration_account_need_to_approve($user)) {
      $message['send'] = FALSE;
    }
  }
}