code: public static void setHost(MailHost mailHost) {
          switch (mailHost) {
              case NE163:
                  host = "smtp.163.com";
                  break;
              case GMAIL:
                  host = "smtp.gmail.com";
                  break;
              case SINA:
                  host = "smtp.sina.com";
                  break;
              case OUTLOOK:
                  host = "smtp-mail.outlook.com";
                  break;
              default:
                  host = "smtp.qq.com";
                  break;
          }
      }
docs: 设置邮件服务器
  
  @param mailHost {@link MailHost}