I got it.

 /engine/lib/users.php

set_user_notification_setting($user->getGUID(), 'email', false);
set_user_notification_setting($user->getGUID(), 'site', true);

;)

I've been looking for the same thing. If someone is interested, it's now here:

/engine/classes/Elgg/Database/UserTable.php

line 434:

        // Turn on email notifications by default
        set_user_notification_setting($user->getGUID(), 'email', true);

Although it might not be the best idea to change the core code, I'm still looking into solving this through a plugin.

The default permission in elgg is logged-in user. So if you created a content and didnt change the permission to "public" then it wont show in the index for non-loggedin users.

oh! Thanks!