For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:p_conrad:branches/openSUSE_Tumbleweed/home:p_conrad:branches.repo
zypper refresh
zypper install amavisd-new
For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:p_conrad:branches/openSUSE_Factory/home:p_conrad:branches.repo
zypper refresh
zypper install amavisd-new
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:p_conrad:branches/15.5/home:p_conrad:branches.repo
zypper refresh
zypper install amavisd-new
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:p_conrad:branches/15.4/home:p_conrad:branches.repo
zypper refresh
zypper install amavisd-new