code: @SuppressWarnings("unchecked")
      private void initSession(SMTPClientSession session) {
          Iterator<SMTPDeliveryEnvelope> transactionList = ((Iterator<SMTPDeliveryEnvelope>) session.getAttribute(SMTP_TRANSACTIONS_KEY));
          SMTPDeliveryEnvelope transaction =  transactionList.next();
          
          session.setAttribute(CURRENT_SMTP_TRANSACTION_KEY,transaction);
          session.setAttribute(RECIPIENTS_KEY, transaction.getRecipients().iterator());
          session.setAttribute(DELIVERY_STATUS_KEY, new ArrayList<DeliveryRecipientStatus>());
  
          // cleanup old attribute
          session.setAttribute(CURRENT_RCPT_KEY, null);
  
      }
docs: Init the SMTPClienSesion by adding all needed data to the attributes
  
  @param session