Для 15.6 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/home:mmeiste/15.6/home:mmeiste.repo
zypper refresh
zypper install offlineimap
Для 15.5 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/home:mmeiste/15.5/home:mmeiste.repo
zypper refresh
zypper install offlineimap
Для 15.4 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/home:mmeiste/15.4/home:mmeiste.repo
zypper refresh
zypper install offlineimap