code: protected void pipelining(SMTPClientSession session) throws SMTPException {
          SMTPDeliveryEnvelope transaction = (SMTPDeliveryEnvelope) session.getAttribute(CURRENT_SMTP_TRANSACTION_KEY);
          
          session.setAttribute(PIPELINING_ACTIVE_KEY, true);
          SMTPPipeliningRequest request = new SMTPPipeliningRequestImpl(transaction.getSender(), transaction.getRecipients().iterator());
          next(session, request);
          
      }
docs: Use the SMTP <code>PIPELINING</code> extension to send the commands to the remote SMTP Server
  
  @param session
  @throws SMTPException