For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:SeaEagle1/openSUSE_Tumbleweed/home:SeaEagle1.repo
zypper refresh
zypper install roundcubemail
For openSUSE Leap 15.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:SeaEagle1/openSUSE_Leap_15.2/home:SeaEagle1.repo
zypper refresh
zypper install roundcubemail
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:SeaEagle1/15.4/home:SeaEagle1.repo
zypper refresh
zypper install roundcubemail