$url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];

if (strpos($url,'this-is-an-example-post') !== false) {
if($_GET['utm_campaign']==testing123 && $_GET['utm_source']==testing456) {
function preserve_qs() {
if (empty($_SERVER['QUERY_STRING']) && strpos($_SERVER['REQUEST_URI'], "?") === false) {
    return "";
}
return "?" . $_SERVER['QUERY_STRING'];
}
header("Location: http://example123.com/this-is-an-example-post" . preserve_qs());
exit;
}
}