yum install 'http://mirror.de-labrusse.fr/NethDev/nethserver-yum-cron/nethserver-yum-cron-0.1.1-1.ns7.sdl.noarch.rpm
then you install yum-cron.
By default, the notifications are sent and you download the updates. All notifications are sent to the admin user, think to install the samba AD or openldap account provider. If you need it, you can direct the notifications on other email addresses, of course I can not do the settings of your smarthost, please verify in /var/log/maillog if you don't receive the emails, why they are bounced.
Each day a cron job starts during the night (after a random sleep time) and looks after update. If you think this time is too long (maximum 360 minutes to wait), we can lower it.