Smanettando un po' sul forum della sun:

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


public class javamaildemo {
  String host = "smtp.mail.yahoo.it"; //tuo smtp
  String from = "xyzabgd@yahoo.it"; //tuo indirizzo email
  String ToAddress = "destinatario@email.com"; //destinatario
  String user = "xyzabgd";
  String pass = "password";
  
  public javamaildemo() {
    try {
      //initialize the StringBuffer object within the try/catch loop
      StringBuffer sb = new StringBuffer( );
      
      //Get system properties
      Properties props = System.getProperties( );
    
      //Setup mail server
      props.put("mail.smtp.host", host);
      props.put("mail.debug", "true");
      props.put("mail.smtp.auth","true");

      //Get session
      Session session = Session.getDefaultInstance(props, null);
      session.setDebug(true);
      session.setPasswordAuthentication(new URLName("smtp",host,25,"INBOX",user,pass), new PasswordAuthentication(user,pass));

      //Define message
      MimeMessage msg = new MimeMessage(session);
      //Set the from address
      msg.setFrom(new InternetAddress(from));
      //Set the to address
      msg.addRecipient(Message.RecipientType.TO, new InternetAddress(ToAddress));
      //Set the subject
      msg.setSubject("Test mail using JavaMail APIs");
      //Set the text content for body
      sb.append("This is the 1st String line.\n\n");
      sb.append("This is the 2nd String line.\n\n");
      sb.append("This is the 3rd String line.\n\n");
      msg.setText(sb.toString( ));  
      //Send message
      Transport tr = session.getTransport("smtp");
      tr.connect(host, user, pass);
      msg.saveChanges(); // don't forget this
      tr.sendMessage(msg, msg.getAllRecipients());
      tr.close();
    }
    catch (MessagingException e) {
      System.out.println(e);
    }
  } 
  
  public static void main(String[] args) {
    javamaildemo jv = new javamaildemo();
  }
}
commenta la prop e session.setDebug se non vuoi vedere il log dei messaggi di debug.