For JFBConnect, to prevent our emails, edit the /components/com_jfbconnect/controllers/loginregister.php file. Look for the following, around line 496:
// Send the registration email.
$return = JFactory::getMailer()->sendMail($data['mailfrom'], $data['fromname'], $data['email'], $emailSubject, $emailBody);Comment out that last line.
In the models/registration.php file in com_users, find the same 2 lines at about 410.
Hope that helps. Either way, let us know how that goes.
Thanks,
Alex