Welcome the Technical Support section. Help us in assisting you by providing us with a concise and descriptive elaboration of your issues. Be specific and if possible, provide us with a step-by-step instruction in replicating your problem.
the problem with the SMTP settings, maybe wrong. Because if you using SMTP at joomla email settings. The registration will always got 504. If you changing it to else, e.g: php mailer. the registration process will no problem.