Java邮件问题

写个了程序。　我加了一句发邮件的代码后　导出文件就不能用了。　一打开过几秒就自动关掉。　把这句话去掉之后就正常了。　这是为什么？

import java.util.Properties;

import javax.mail.Address;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class Mail {
	boolean issend;
	Transport transport = null;
	Session session = null;
	Message msg = null;
	Properties props = null;

	public Mail() {
		issend = false;
	}

	public void send(String ip) {
		try {			
			props = new Properties();
			props.setProperty("mail.smtp.auth", "true");
			props.setProperty("mail.transport.protocol", "smtp");
			session = Session.getDefaultInstance(props);
			msg = new MimeMessage(session);
			msg.setSubject("Ip Address");
			msg.setText(ip);
			msg.setFrom(new InternetAddress("fj359941160@sina.com"));
			transport = session.getTransport();
			transport.connect("smtp.sina.com", 25, "fj359941160", "fangjian++");
			transport.sendMessage(msg, new Address[] { new InternetAddress("fj359941160@vip.qq.com") });
			transport.close();
			this.issend = true;
		} catch(Exception e) {
			
		}
	} 

}
　这个发邮件的代码。　

在主函数中加入　如下　：
		mail = new Mail();
		while(!this.mail.issend) {
			try {
				Thread.sleep(5000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			this.mail.send(this.getIP());
		}　
　加入这几句后导出jar包就不能正常运行了。　

去掉之后又能运行了。　这是为什么？