docs: def _getsender():
      """Return local sender.
      Don't use the getpass module, it looks at various environment variables
      and is unreliable.
      """
      import os
      import pwd
      import socket
      host = socket.gethostname()
      user = pwd.getpwuid(os.getuid())[0]
      return "%s@%s" % (user, host)