code: @Override
      public void acknowledge(SQSMessage message) throws JMSException {
          session.checkClosed();
  
          SQSMessageIdentifier ackMessage = SQSMessageIdentifier.fromSQSMessage(message);
  
          int indexOfMessage = indexOf(ackMessage);
  
          /**
           * In case the message has already been deleted, warn user about it and
           * return. If not then then it should continue with acknowledging all
           * the messages received before that
           */
          if (indexOfMessage == -1) {
              LOG.warn("SQSMessageID: " + message.getSQSMessageId() + " with SQSMessageReceiptHandle: " +
                       message.getReceiptHandle() + " does not exist.");
          } else {
              bulkAction(getUnAckMessages(), indexOfMessage);
          }
      }
docs: Acknowledges all the consumed messages as well as the previously consumed
  messages on the session via calling <code>deleteMessageBatch</code> until
  all the messages are deleted.