For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h/openSUSE_Tumbleweed/home:manfred-h.repo
zypper refresh
zypper install dovecot23
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h/openSUSE_Slowroll/home:manfred-h.repo
zypper refresh
zypper install dovecot23
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h/16.0/home:manfred-h.repo
zypper refresh
zypper install dovecot23