docs: def get_configfile():
      """Return full path to configuration file.
  
       - Linux: ~/.local/share/pyfilemail
       - OSX: ~/Library/Application Support/pyfilemail
       - Windows: C:\\\Users\\\{username}\\\AppData\\\Local\\\pyfilemail
  
       :rtype: str
      """
  
      ad = appdirs.AppDirs('pyfilemail')
      configdir = ad.user_data_dir
      configfile = os.path.join(configdir, 'pyfilemail.cfg')
  
      return configfile