old_contents: from django.apps import AppConfig
  from django.utils.translation import gettext_lazy as _
  
  
  class PostOfficeConfig(AppConfig):
      name = 'post_office'
      verbose_name = _("Post Office")
  
      def ready(self):
          from post_office import tasks
          from post_office.settings import get_celery_enabled
          from post_office.signals import email_queued
  
          if get_celery_enabled():
              email_queued.connect(tasks.queued_mail_handler)
  
new_contents: from django.apps import AppConfig
  from django.utils.translation import gettext_lazy as _
  
  
  class PostOfficeConfig(AppConfig):
      name = 'post_office'
      verbose_name = _("Post Office")
      default_auto_field = 'django.db.models.AutoField'
  
      def ready(self):
          from post_office import tasks
          from post_office.settings import get_celery_enabled
          from post_office.signals import email_queued
  
          if get_celery_enabled():
              email_queued.connect(tasks.queued_mail_handler)
  
subject: Set the default autofield for the app (#401)