有关javamail的错误AuthenticationFailedException（急）

我想请问AuthenticationFailedException错误出现是什么引起的，下面是一个利用javamail发送附件的源程序。

package Mybean;
import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;

public class AttachExample {
public void postemail(String tomail, String fileurl)
throws Exception {
String host ="smtp.163.com" ;
String from ="*****@163.com";
String to = tomail;
String fileAttachment = fileurl; //附件地址

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

// Setup mail server
props.put("mail.smtp.host", host);
props.put("mail.smtp.auth", "true");

// Get session
Session session =
Session.getInstance(props, null);

transport = session.getTransport("smtp");
transport.connect("smtp.163.com","*****","****");

// Define message
MimeMessage message =
new MimeMessage(session);
message.setFrom(
new InternetAddress(from));
message.addRecipient(
Message.RecipientType.TO,
new InternetAddress(to));
message.setSubject(
"Here is Javacert!");

// create the message part
MimeBodyPart messageBodyPart =
new MimeBodyPart();

//fill message
messageBodyPart.setText("your cert");

Multipart multipart = new MimeMultipart();
multipart.addBodyPart(messageBodyPart);

// Part two is attachment
messageBodyPart = new MimeBodyPart();
DataSource source =
new FileDataSource(fileAttachment);
messageBodyPart.setDataHandler(
new DataHandler(source));
messageBodyPart.setFileName(fileAttachment);
multipart.addBodyPart(messageBodyPart);

// Put parts in message
message.setContent(multipart);

// Send the message
Transport.send( message );
}
}