default / sysconfig files gone - How to configure this options now?

Release Notes for 8.6.1 states:

Starting with we have stopped installing /etc/default/kopano (for Debian based distributions) and /etc/sysconfig/kopano (for rpm based distributions).

This files provided some config options,
How to configure this options now?

If you want to configure one of the options defined in these files, you still need to configure them in these files (they should also stay for upgrades). You can find an example config in /use/share/doc/kopano/example-config (typed from memory)

I had the same issue and solved it by copying the required configuration templates from the following directory: /usr/share/doc/kopano/example-config. Some of the files could just be copied using cp and other were compressed (those ending with .gz), so I had to use the gunzip command like this:
gunzip -c /usr/share/doc/kopano/example-config/server.cfg.gz | tee /etc/kopano/server.cfg