code: def process_response(self, request, response):
          
          if response.status_code == 404 and not settings.DEBUG:
              domain = request.get_host()
              path = request.get_full_path()
              referer = force_text(
                  request.META.get('HTTP_REFERER', ''), errors='replace')
  
              if not self.is_ignorable_request(request, path, domain, referer):
                  ua = request.META.get('HTTP_USER_AGENT', '<none>')
                  ip = request.META.get('REMOTE_ADDR', '<none>')
  
                  user = None
                  if request.user and hasattr(request.user, 'email'):
                      user = request.user.email
                  content = (
                      "Referrer: %s\n"
                      "Requested URL: %s\n"
                      "User agent: %s\n"
                      "IP address: %s\n"
                      "User: %s\n"
                  ) % (referer, path, ua, ip, user)
                  if self.is_internal_request(domain, referer):
                      internal = 'INTERNAL '
                  else:
                      internal = ''
                  mail_managers(
                      "Broken %slink on %s" % (
                          internal,
                          domain
                      ),
                      content,
                      fail_silently=True)
          return response
docs: Send broken link emails for relevant 404 NOT FOUND responses.