code: public void close() {
      for (ProbeSender sender : getSenders()) {
        try {
          sender.close();
        } catch (TransportException e) {
          LOGGER.warn( "Issue closing the ProbeSender [" + sender.getDescription() + "]", e);
        }
      }
    }
docs: This closes any of the underlying resources that a ProbeSender might be
  using, such as a connection to a server somewhere.