code: @Override
      public SMTPClientFuture<FutureResult<Collection<SMTPResponse>>> send(SMTPPipeliningRequest request) {
          SMTPClientFutureImpl<FutureResult<Collection<SMTPResponse>>> future = new SMTPClientFutureImpl<FutureResult<Collection<SMTPResponse>>>(false);
          future.setSMTPClientSession(this);
          AggregationListener listener = new AggregationListener(future, request.getRequests().size());
          for(SMTPRequest req: request.getRequests()) {
              send(req).addListener(listener);
          }
          return future;
      }
docs: Implementation which just send each {@link SMTPRequest} which is hold in the {@link SMTPPipeliningRequest#getRequests()} method via
  {@link #send(SMTPRequest)} method.