How do we check if postfix.org is down?
We determine if postfix.org is down by performing a server check from our servers, in a way that is similar to how your web browser (e.g. Chrome, Safari, Firefox) would make a connection to the website. This server check is performed from an edge node closest to you, from a network that is present in over 285 cities and 100+ countries. We then check the server status code returned to show you if postfix.org is up or down.
What server response codes do we consider "down" or indicate a problem?
We indicate that postfix.org is down if it returns an HTTP status code anywhere within the 4xx or 5xx range. For example, a "not found" error would return a status code of 404, so we would mark the site as down.
What server response codes do we consider "up" / accessible?
We mark a website as up if it returns an HTTP status code anywhere within the 2xx or 3xx ranges. For example, most sites will respond with a 200 HTTP code, so we would mark that site as up. If the site returns a successful status code, but the content or body of the page is returning an error or otherwise not working correctly, we won't be able to detect that and our site may show a false negative. In those cases you may want to contact the site owner to notify them of the problem.