I have a daily cron running with php /var/www/cloud.example.com/updater/updater.phar --no-interaction && php /var/www/cloud.example.com/occ upgrade to update my nextcloud automatically. But now I would like to get an email notification, when an update has applied. Perhaps included with a changelog of the update.
Is there any build in in nextcloud?
If your system is able to send mails just set variable "MAILTO=me@example.com" in your cronjob file. Output of this crontab will be send to your email address.
yes, but not only when there is an update available, but everytime 
And I don’t know if the changelog really is included, didn’t have a auto update in between. Just updated manually to NC13…