This can be easily achieved by adding the following code to the top of offline.php, either in the 'system' template or if you're over-riding this file with your own template, then in your own offline.php file:
Code: Select all
<?php header('HTTP/1.1 503 Service Temporarily Unavailable',true,503); header('Status: 503 Service Temporarily Unavailable'); header('Retry-After: 86400'); ?>
Perhaps this should be standard in the Joomla! 'system' template?