Ticket #21143: sunrise.php

<?php

function my_no_blog_redirect( $domain, $blogname, $current_site, $current_blog, $path ) {

        // If we are here then a valid blog hasn't been found for this request

        // Perform our own checking to see if   we need to do a 301 redirect from the requested domain to another domain
        $domain_redirect = domain_redirect_location_lookup( $domain, $blogname, $current_site, $current_blog, $path );

        if ($domain_redirect) {
                header( "HTTP/1.1 301 Moved Permanently" );
                header( "Location: http://{$domain_redirect}{$_SERVER['REQUEST_URI']}" );
                exit;
        }
        // Otherwise WordPress will fall back to using the NOBLOGREDIRECT constant
}
add_action('no_blog_redirect', 'my_no_blog_redirect', 10, 5 );