必须按照 发送电子邮件指南:

def create_message(sender, to, subject, message_text):
  message = MIMEText(message_text)
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject
  return {'raw': base64.urlsafe_b64encode(message.as_string())}

def main():
  credentials = get_credentials()
  http = credentials.authorize(httplib2.Http())
  service = discovery.build('gmail', 'v1', http=http)
  message = create_message(
    'sender@gmail.com', 'receiver@gmail.com', 'Subject', 'Message text'
  )
  send_message(service, 'me', message)