HTTP status codes are server responses through which the server states what happened to the requested address. Distinguishing between codes has a direct impact on indexing. A success code means the content exists. A permanent redirect is used when an address changes and passes signals on to the new page, while a temporary redirect is used only when the content will genuinely return to its original location. The code for a non-existent page belongs to discontinued addresses; if you know content has been removed permanently, there is also a more unambiguous code, after which the search engine removes the page from the index more quickly. Particularly important is the code for temporary unavailability during a planned outage – if the server instead returns an error, or an empty page with a success code, you risk having the content dropped from the index.
See also: Soft 404, Redirect chains, Website migration without losing rankings.
