code: public static void sendMail(String to, String title, String content) throws Exception {
          if (!Checker.isEmail(to)) {
              throw new Exception("this email address is not valid. please check it again");
          }
          // 获取系统属性
          Properties properties = System.getProperties();
          // 设置邮件服务器
          properties.setProperty("mail.smtp.host", host);
          if (port > 0) {
              properties.setProperty("mail.smtp.port", String.valueOf(port));
          }
          properties.put("mail.smtp.auth", "true");
          MailSSLSocketFactory sf;
          sf = new MailSSLSocketFactory();
          sf.setTrustAllHosts(true);
          properties.put("mail.smtp.ssl.enable", sslEnable);
          properties.put("mail.smtp.ssl.socketFactory", sf);
          // 获取session对象
          Session session = Session.getInstance(properties, new Authenticator() {
              @Override
              public PasswordAuthentication getPasswordAuthentication() {
                  // 发件人邮件用户名、密码
                  return new PasswordAuthentication(from, key);
              }
          });
  
          // 创建默认的MimeMessage对象
          MimeMessage message = new MimeMessage(session);
          // Set From:头部头字段
          message.setFrom(new InternetAddress(from, personal, "UTF-8"));
          // Set To:头部头字段
          message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
          // Set Subject:头部头字段
          message.setSubject(title, "UTF-8");
          // 设置消息体
          message.setContent(content, "text/html;charset=UTF-8");
          message.setSentDate(new Date());
          // 发送消息
          Transport.send(message);
      }
docs: 发送邮件，调用此方法前请先检查邮件服务器是否已经设置，如果没有设置，请先设置{@link MailSender#setHost(String)}， 如不设置将使用默认的QQ邮件服务器
  
  @param to 收件箱
  @param title 标题
  @param content 内容
  
  @throws Exception 异常