### Integrate Kopano Core Repository
### Retrieve <license key>
### Subscription customers at login
$ sudo su
[...]
# URL=https://serial:<license key>@download.kopano.io/supported/core:/final/Ubuntu_18.04/
# echo "deb $URL /">> /etc/apt/sources.list.d/kopano.list
# curl $URL/Release.key | apt-key add -
# apt install apt-transport-https
# apt update
### Install Kopano Core packages
# apt install kopano-server-packages
# exit