Other components can be added as well of course.
Make sure to have the package apt-transport-httpsinstalled
For Debian-based distributions, we recommend to import the key as well. These keys are the same for all components, so only need needs to be imported once.
curl https://serial:ENTERYOURSERIALHERE@download.kopano.io/supported/core:/final/Debian_8.0/Release.key | apt-key add -