old_contents: import os
  from distutils.util import strtobool
  
  
  SECRET_KEY = os.getenv('SECRET_KEY', None)
  
  SERVER_NAME = os.getenv('SERVER_NAME',
                          'localhost:{0}'.format(os.getenv('DOCKER_WEB_PORT',
                                                           '8000')))
  
  # Flask-Mail.
  MAIL_SERVER = os.getenv('MAIL_SERVER', 'smtp.gmail.com')
  MAIL_PORT = os.getenv('MAIL_PORT', 587)
  MAIL_USE_TLS = bool(strtobool(os.getenv('MAIL_USE_TLS', 'true')))
  MAIL_USE_SSL = bool(strtobool(os.getenv('MAIL_USE_SSL', 'false')))
  MAIL_USERNAME = os.getenv('MAIL_USERNAME', None)
  MAIL_PASSWORD = os.getenv('MAIL_PASSWORD', None)
  MAIL_DEFAULT_SENDER = os.getenv('MAIL_DEFAULT_SENDER', 'smtp.gmail.com')
  
  # Celery.
  CELERY_BROKER_URL = os.getenv('CELERY_BROKER_URL', 'redis://redis:6379/0')
  CELERY_RESULT_BACKEND = CELERY_BROKER_URL
  CELERY_ACCEPT_CONTENT = ['json']
  CELERY_TASK_SERIALIZER = 'json'
  CELERY_RESULT_SERIALIZER = 'json'
  CELERY_REDIS_MAX_CONNECTIONS = 5
  
new_contents: import os
  from distutils.util import strtobool
  
  
  SECRET_KEY = os.getenv('SECRET_KEY', None)
  
  SERVER_NAME = os.getenv('SERVER_NAME',
                          'localhost:{0}'.format(os.getenv('DOCKER_WEB_PORT',
                                                           '8000')))
  
  # Flask-Mail.
  MAIL_SERVER = os.getenv('MAIL_SERVER', 'smtp.gmail.com')
  MAIL_PORT = os.getenv('MAIL_PORT', 587)
  MAIL_USE_TLS = bool(strtobool(os.getenv('MAIL_USE_TLS', 'true')))
  MAIL_USE_SSL = bool(strtobool(os.getenv('MAIL_USE_SSL', 'false')))
  MAIL_USERNAME = os.getenv('MAIL_USERNAME', None)
  MAIL_PASSWORD = os.getenv('MAIL_PASSWORD', None)
  MAIL_DEFAULT_SENDER = os.getenv('MAIL_DEFAULT_SENDER', 'contact@local.host')
  
  # Celery.
  CELERY_BROKER_URL = os.getenv('CELERY_BROKER_URL', 'redis://redis:6379/0')
  CELERY_RESULT_BACKEND = CELERY_BROKER_URL
  CELERY_ACCEPT_CONTENT = ['json']
  CELERY_TASK_SERIALIZER = 'json'
  CELERY_RESULT_SERIALIZER = 'json'
  CELERY_REDIS_MAX_CONNECTIONS = 5
  
subject: Fix default MAIL_DEFAULT_SENDER value