Notifies the network admin that a new user has been activated.
<?php newuser_notify_siteadmin( $user_id ) ?>
Filter 'newuser_notify_siteadmin' to change the content of the notification email. Filter function is passed $msg (the email message text), $user (a WP_User object for the new user)
Since: MU
newuser_notify_siteadmin() is located in wp-includes/ms-functions.php