Simple WordPress function / plugin to redirect a site

While the plugin might solve your problem you could try something direct with WordPress API:

add_action( 'template_redirect', 'wpse_142191_all_redirect' );
function wpse_142191_all_redirect() {
    if ( !is_user_logged_in() ) {
        wp_redirect( 'http://other-site.com', 301); 
            exit; //always die or exit after redirect
    }
}

Be careful with it,this will redirect the whole site on the home page of other site. I added a condition, maybe you do not want to be redirect as a user of website.