Why are the HTTP headers important for SEO?
The HTTP headers being the first information that a robot gets when it tries to visit a page, it is necessary to set up correctly your server and scripts in order to make sure to send the right information.
It would be way too long to comment all the existing codes.
The most important is to send a header that exactly corresponds to the situation. Here are the most common and important headers related to SEO optimization:
200 means that the server delivers correctly the requested information.
404 means that requested resource no longer exists.
301 indicates that the requested resource is permanently accessible through another URL. Perfectly adapted during a massive change of URLs, as part of a major redesign or a change of domain, for example.
302 indicates that the requested resource is temporarily accessible through another URL.
Others that are less famous may be very important.
410 indicates that the requested resource no longer exists. It is very often used instead of 404.
510 indicates that the requested resource is temporarily unavailable. Very useful during maintenance or overload.