How long is the life of SendMail.class ?

I'm new with the servlet and all other wep application stuff so sorry if I
ask a wierd queston. I have next code which work fine:

package pascalpozega;

import java.util.*;
import java.io.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;

/**
 * msgsendsample creates a very simple text/plain message and sends it.
 * <p>
 * usage: <code>java msgsendsample <i>to from smtphost true|false</i></code>
 * where <i>to</i> and <i>from</i> are the destination and
 * origin email addresses, respectively, and <i>smtphost</i>
 * is the hostname of the machine that has the smtp server
 * running. The last parameter either turns on or turns off
 * debugging during sending.
 *
 * @author Max Spivak
 */
public class SendMail {
    static String msgText = "Hi,\nPlease - .\nJohn";
    public static boolean jelPoslan = true;
    public static String greska = "";

    public static void main(String[] args) throws Exception {
        sendMail("support@eatj.com", "johnzhang@xyax.com", "Hi", msgText);

        /*
        if (args.length != 4) {
            usage();
            System.exit(1);
        }

        System.out.println();

        String to = args[0];
        String from = args[1];
        String host = args[2];
        boolean debug = Boolean.valueOf(args[3]).booleanValue();

        // create some properties and get the default Session
        Properties props = new Properties();
        props.put("mail.smtp.host", host);
        if (debug) props.put("mail.debug", args[3]);

        Session session = Session.getDefaultInstance(props, null);
        session.setDebug(debug);

        // create a message
        Message msg = new MimeMessage(session);
        msg.setFrom(new InternetAddress(from));
        InternetAddress[] address = {new InternetAddress(args[0])};
        msg.setRecipients(Message.RecipientType.TO, address);
        msg.setSubject("JavaMail APIs Test");
        msg.setSentDate(new Date());
        // If the desired charset is known, you can use
        // setText(text, charset)
        msg.setText(msgText);

        Transport.send(msg);
         */

    }

    public static void sendMail(String to, String from, String subject,
String content) throws Exception {
        sendMail(to, from, subject, content, "localhost");
    }

    public static void sendMail(String to, String from, String subject,
String content, String host) throws Exception {
        // create some properties and get the default Session

        host = "localhost";

        Properties props = new Properties();
        props.put("mail.smtp.host", host);

        Session session = Session.getDefaultInstance(props, null);

        try {
            // create a message
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress(from));
   msg.setHeader("Content-Type", "text/plain; charset=windows-1250");
            InternetAddress[] address = {new InternetAddress(to)};
            msg.setRecipients(Message.RecipientType.TO, address);
            msg.setSubject(subject,"windows-1250");
   //msg.setHeader("Content-Transfer-Encoding", "8bit");

            msg.setSentDate(new Date());
            // If the desired charset is known, you can use
            // setText(text, charset)
            //msg.setText(content,"Cp1250");
            msg.setText(content,"windows-1250");

            Transport.send(msg);
            msg = null;
        } catch (MessagingException mex) {

            System.out.println("\n--Exception handling in
msgsendsample.java");

            mex.printStackTrace();
            System.out.println();
            Exception ex = mex;
            greska = ex.toString();
            jelPoslan = false;
            ex = null;

            do {
                if (ex instanceof SendFailedException) {
                    SendFailedException sfex = (SendFailedException)ex;
                    Address[] invalid = sfex.getInvalidAddresses();
                    if (invalid != null) {
                        System.out.println(" ** Invalid Addresses");

                        if (invalid != null) {
                            for (int i = 0; i < invalid.length; i++)
                                System.out.println(" " +
invalid[i]);
                        }
                    }
                    Address[] validUnsent = sfex.getValidUnsentAddresses();
                    if (validUnsent != null) {
                        System.out.println(" ** ValidUnsent Addresses");
                        if (validUnsent != null) {
                            for (int i = 0; i < validUnsent.length; i++)
                                System.out.println("
"+validUnsent[i]);
                        }
                    }
                    Address[] validSent = sfex.getValidSentAddresses();
                    if (validSent != null) {
                        System.out.println(" ** ValidSent Addresses");
                        if (validSent != null) {
                            for (int i = 0; i < validSent.length; i++)
                                System.out.println("
"+validSent[i]);
                        }
                    }
                }
                System.out.println();
                if (ex instanceof MessagingException)
                    ex = ((MessagingException)ex).getNextException();
                else
                    ex = null;
            } while (ex != null);

        }
    }

    private static void usage() {
        System.out.println("usage: java msgsendsample <to> <from> <smtp>
true|false");
    }
}

Iif visitor enter wrong adress I got

javax.mail.SendFailedException: Sending failed; nested exception is: class
javax.mail.MessagingException: 553 5.5.4 ... Domain name required for sender
address MARIONET.HR

and its OK, but it if I again enter right mail address I got the same
exception. How it memory wrong adress when I instance new SendMail class?

p.s.
What I need to setup so that I can experiment on my computer? So that I
don't have to upload SendMail.class every time I cahnged it.