ClassNot found error

this is my class

package MyMail;

import java.util.*;
import javax.mail.*;
import javax.mail.internet.*; 
public class SendMail {

public static void main(String args[]) throws Exception {

try{
        String host = "192.168.10.205";
        String from = "test@localhost";
        String to = "test@localhost";

// Get system properties
        Properties properties = System.getProperties();

// Setup mail server
       properties.setProperty("mail.smtp.host", host);

// Get the default Session object.
        Session session = Session.getDefaultInstance(properties);

// Create a default MimeMessage object.
        MimeMessage message = new MimeMessage(session);

// Set the RFC 822 "From" header field using the
        // value of the InternetAddress.getLocalAddress method.
        message.setFrom(new InternetAddress(from));

// Add the given addresses to the specified recipient type.
        message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

// Set the "Subject" header field.
        message.setSubject("hi..!");

// Sets the given String as this part's content,
        // with a MIME type of "text/plain".
        message.setText("Hi ......");

// Send message
        Transport.send(message);

System.out.println("Message Send.....");
    	}catch(Exception e){
    		e.printStackTrace();
    	}
    }
}

this is the error i got .what else i need to add?

this example i got from web site

Hi!
Try switching to JRE 6, which includes the javax.activation.DataSource interface, or use mr Dittmer's excellent tactic described below.
I can recommend http://jarfinder.com/ to help you find JAR files in which a given class/interface is located.
Best wishes!

There's no need to switch to Java 6, really - the jar file for JAF can be downloaded from java.sun.com, and works fine with earlier Java versions.

i added mail.jar and activation.jar files to the project.then i run the file.But it gives this error after taking sometimes.

Exception in thread "main" javax.mail.MessagingException: Could not connect to SMTP host: 192.168.10.205, port: 25;
  nested exception is:
	java.net.SocketException: Network is unreachable: connect
	at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1545)
	at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:453)
	at javax.mail.Service.connect(Service.java:291)
	at javax.mail.Service.connect(Service.java:172)
	at javax.mail.Service.connect(Service.java:121)
	at javax.mail.Transport.send0(Transport.java:190)
	at javax.mail.Transport.send(Transport.java:120)
	at my.SendMail.main(SendMail.java:41)
Caused by: java.net.SocketException: Network is unreachable: connect
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.PlainSocketImpl.doConnect(Unknown Source)
	at java.net.PlainSocketImpl.connectToAddress(Unknown Source)
	at java.net.PlainSocketImpl.connect(Unknown Source)
	at java.net.SocksSocketImpl.connect(Unknown Source)
	at java.net.Socket.connect(Unknown Source)
	at java.net.Socket.connect(Unknown Source)
	at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:267)
	at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:227)
	at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1511)
	... 7 more

Either port 25 is closed on 192.168.10.205, or 192.168.10.205 cannot be reached at all. The error message "Network is unreachable" makes me think the latter is the case.

Are you sure that a) you can reach that IP address at all, and b) there is a mail server running on that machine?