Basically in joomla there are two types of registration done!
Using Activation.(User get's an email with login details and activation link)
Without activation. (user get’s an email just with username and confirming the registration)
Method three: (stop both these emails)
I found if you want to disable the annoying email when a front end user joins your site, I had to alter:
/administrator/components/com_users/controller.php Line 522
comment out:
//JUtility::sendMail($mailfrom, $fromname, $row->email, $subject2, $message2);