Redirect 404.php to URL outside the site?

CMS & WordPress
3

The reason why PHP redirection doesn’t work is, that because this part of code should be set on beggining of document, just before <!doctype>.Maybe you can do something like this:

Go into header.php, at the beggining of file add this:

 <?php
    if ( is_404() ) {
        header("HTTP/1.1 301 Moved Permanently");
        header("Location:http://www.exmaple.com/");
    } 
 ?>

EDIT: Sorry on wrong reply.