For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:gladiac:mailman/openSUSE_Tumbleweed/home:gladiac:mailman.repo
zypper refresh
zypper install python-postorius
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:gladiac:mailman/16.0/home:gladiac:mailman.repo
zypper refresh
zypper install python-postorius
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:gladiac:mailman/15.6/home:gladiac:mailman.repo
zypper refresh
zypper install python-postorius