直接使用MimeMessage发送中文邮件，收件人往往会收到乱码，必须在发送前做字符集的声明。例子如下：

      Session mailSession = Session.getInstance(props,
        new javax.mail.Authenticator() {
         protected PasswordAuthentication getPasswordAuthentication() {
          return new PasswordAuthentication(userName,
            password);
         }
        });

      Message message = new MimeMessage(mailSession);      //创建新的MimeMessage邮件实例
      
      message.setFrom(new InternetAddress("sender@sina.com","发件人名称","utf-8"));  //设置发件人邮箱地址和名称
      message.setRecipients(Message.RecipientType.TO,
        InternetAddress.parse("receiver@sina.com"));       //设置收件人邮箱地址
      
      message.setSubject(MimeUtility.encodeText("中文邮件标题", "utf-8", "B"));  //生成邮件标题
       
      String strText="中文文件正文";        //输入邮件正文内容
      
      message.setContent(strText, "text/plain;charset=utf-8");   //生成邮件正文     
      
      Transport.send(message);         //发送邮件