Check uddeim.php line 676:
function uddeIMsaveMessage($myself, $to_name, $to_id, $pmessage, $tobedeleted, $tobedeletedsent, $forceembedded, $item_id, $messageid, $copytome, $addccinfo, $sendeform_showallusers, $cryptpass, $backto, $config)
When $messageid>0 then it is a reply.
uddeIM & uddePF Development
CB Language Workgroup
CB 3rd Party Developer