Para openSUSE Tumbleweed execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:hencke/openSUSE_Tumbleweed/home:hencke.repo
zypper refresh
zypper install davmail
Para 15.6 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:hencke/15.6/home:hencke.repo
zypper refresh
zypper install davmail
Para 15.5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:hencke/15.5/home:hencke.repo
zypper refresh
zypper install davmail