I am stupid, why not just return an HTML document explaining the issue, when there is such an incorrect second request in 20 minutes, then blocking that IP for 24 hours? The feed reader software author has to react, otherwise its users will complain to him, no?
Most readers presumably keep showing the last valid response when they get an error, so that the user doesn’t notice. Returning a fake ok response, explaining that the reader is dumb, will lift attention to the user. Not that I would advocate for this solution, except for desperate moments.
