For openSUSE Leap 42.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:STABLE/openSUSE_Leap_42.3/server:Kolab:STABLE.repo
zypper refresh
zypper install kolab
For openSUSE Leap 15.1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:STABLE/openSUSE_Leap_15.1/server:Kolab:STABLE.repo
zypper refresh
zypper install kolab
For openSUSE Leap 15.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:STABLE/openSUSE_Leap_15.0/server:Kolab:STABLE.repo
zypper refresh
zypper install kolab
For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:STABLE/openSUSE_Factory/server:Kolab:STABLE.repo
zypper refresh
zypper install kolab