Custom 404 page - does it need a 404 header?

Question

In my project, I'm routing all requests to index.php. Then I check $_SERVER['REQUEST_URI'] against a whitelist and display the relevent content.

Now, if the $_SERVER['REQUEST_URI'] does not match anything in my whitelist, I display some "page not found" text. In effect, it is a custom 404 error page.

My question is: do I need to write header('HTTP/1.0 404 Not Found'); before I output my HTML? What does it actually do? My error page is displayed regardless so is it important in this scenario?

Answer 1

Yes. That header is used by search engines, and others, to know the status of a page and act accordingly. (eg remove that page from their index, etc)