For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:cschweingruber:branches:server:mail/openSUSE_Tumbleweed/home:cschweingruber:branches:server:mail.repo
zypper refresh
zypper install courier-imap
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:cschweingruber:branches:server:mail/15.5/home:cschweingruber:branches:server:mail.repo
zypper refresh
zypper install courier-imap
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:cschweingruber:branches:server:mail/15.4/home:cschweingruber:branches:server:mail.repo
zypper refresh
zypper install courier-imap
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:cschweingruber:branches:server:mail/15.3/home:cschweingruber:branches:server:mail.repo
zypper refresh
zypper install courier-imap