For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:php:applications/openSUSE_Slowroll/server:php:applications.repo
zypper refresh
zypper install squirrelmail-beta
For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:php:applications/openSUSE_Factory/server:php:applications.repo
zypper refresh
zypper install squirrelmail-beta
For devel languages php tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:php:applications/devel_languages_php_tumbleweed/server:php:applications.repo
zypper refresh
zypper install squirrelmail-beta
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:php:applications/15.6/server:php:applications.repo
zypper refresh
zypper install squirrelmail-beta
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/server:php:applications/15.5/server:php:applications.repo
zypper refresh
zypper install squirrelmail-beta