Java实现邮件发送遇到的问题

mail.smtp.starttls.enable = true

package com.zhyea.zytools;
 
import java.util.Date;
import java.util.Properties;
 
import javax.mail.Message;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
 
public class MailSender {
 
  private static final String MAIL_SMTP_HOST = "smtp.exmail.qq.com";
  private static final Integer MAIL_SMTP_PORT = 587;
  private static final Boolean MAIL_SMTP_AUTH = true;
  private static final String MAIL_SMTP_USER = "robin@zhyea.com";
  private static final String MAIL_SMTP_PASSWORD = "robinzhyea";
 
  private static Properties props = new Properties();
 
  static {
    props.put("mail.smtp.host", MAIL_SMTP_HOST);
    props.put("mail.smtp.auth", MAIL_SMTP_AUTH);
    props.put("mail.smtp.user", MAIL_SMTP_USER);
    props.put("mail.smtp.password", MAIL_SMTP_PASSWORD);
    props.put("mail.smtp.starttls.enable", true);
  }
 
 
  /**
   * 发送邮件
   */
  public static void send(String to, String title, String content) {
    try {
      Session session = Session.getInstance(props);//创建邮件会话
      MimeMessage message = new MimeMessage(session);//由邮件会话新建一个消息对象
 
      message.setFrom(new InternetAddress(MAIL_SMTP_PASSWORD));//设置发件人的地址
      message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));//设置收件人,并设置其接收类型为TO
      //设置信件内容
      //message.setText(mailContent); //发送 纯文本 邮件 TODO
      message.setSubject(title);//设置标题
      message.setContent(content, "text/html;charset=gbk"); //发送HTML邮件，内容样式比较丰富
      message.setSentDate(new Date());//设置发信时间
      message.saveChanges();//存储邮件信息
 
      //发送邮件
      Transport transport = session.getTransport("smtp");
      transport.connect(MAIL_SMTP_USER, MAIL_SMTP_PASSWORD);
      transport.sendMessage(message, message.getAllRecipients());//发送邮件,其中第二个参数是所有已设好的收件人地址
      transport.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  
}