I want to install kolab 16 on debian 11. There are no specific installation documentation for debian 10. So I follow the installation description for debian 10 on https://docs.kolab.org/installation-guide/debian-10.html. Only the `/etc/apt/sources.list.d/kolab.list` I have filled with the repository URLs of debian 11:
```
deb http://obs.kolabsys.com/repositories/Kolab:/16/Debian_11.0/ ./
deb-src http://obs.kolabsys.com/repositories/Kolab:/16/Debian_11.0/ ./
```
But I cannot install kolab, because the package `roundcubemail-plugins-kolab` is not in the debian 11 repository.
As workaround I can add the debian 10 repository to `/etc/apt/sources.list.d/kolab.list` (which seems to work):
```
deb http://obs.kolabsys.com/repositories/Kolab:/16/Debian_11.0/ ./
deb http://obs.kolabsys.com/repositories/Kolab:/16/Debian_10.0/ ./
deb-src http://obs.kolabsys.com/repositories/Kolab:/16/Debian_11.0/ ./
deb-src http://obs.kolabsys.com/repositories/Kolab:/16/Debian_10.0/ ./
```
But I think the better solution should be if `roundcubemail-plugins-kolab` is also avaliable in the repository for debian 11.