code: public static SystemMail createSystemMail() throws IllegalAccessException {
          if (!exists) {
              SystemMail permissionManager = new SystemMail();
              exists = true;
              return permissionManager;
          }
  
          throw new IllegalAccessException("Cannot create more than one instance of Mail");
      }
docs: Creates a SystemMail. There can only be one single SystemMail, so calling this method twice
  will cause an illegal access exception.
  
  @return a Mail object
  @throws IllegalAccessException thrown if this method is called more than once