code: func (s *WMailServer) Init(shh *whisper.Whisper, path string, password string, pow float64) error {
  	var err error
  	if len(path) == 0 {
  		return fmt.Errorf("DB file is not specified")
  	}
  
  	if len(password) == 0 {
  		return fmt.Errorf("password is not specified")
  	}
  
  	s.db, err = leveldb.OpenFile(path, &opt.Options{OpenFilesCacheCapacity: 32})
  	if err != nil {
  		return fmt.Errorf("open DB file: %s", err)
  	}
  
  	s.w = shh
  	s.pow = pow
  
  	MailServerKeyID, err := s.w.AddSymKeyFromPassword(password)
  	if err != nil {
  		return fmt.Errorf("create symmetric key: %s", err)
  	}
  	s.key, err = s.w.GetSymKey(MailServerKeyID)
  	if err != nil {
  		return fmt.Errorf("save symmetric key: %s", err)
  	}
  	return nil
  }
docs: // Init initializes the mail server.