Although "with systemd" is queried here, and from a logical point of view systemd "Requires (pre):% insserv_prereq" should not be evaluated, it will. The build requires insserv and breaks off on Tumbleweed.
Either you throw the insserv completely out of the spec or you fix the error that Requires is correctly evaluated in an if loop.
Looks more like the bcond and evaluation of %{with systemd} is wrong. Both the server side build service as well as rpmbuild need to understand if you want to build "with systemd" or not. This block from the specfile does not look right to me: %if %{defined systemd_requires} %global with_systemd 1 %endif %bcond_with systemd BTW, if branches are not loops. Do you really need to support builds without systemd nowadays? But, even if you decide to fix it: Running a mail server with a software package maintained by one or two random people, who only marginally care, is not a good idea. I made this experience the hard way: Ubuntu ships a lot of packages, which it inherits from Debian, but does not care for updates in supposedly still maintained distros. The roundcube packages in 18.04 LTS and 20.04 LTS are grossly outdated, exhibit security vulnerabilities and there are no maintainers who care. They even have open bugs about it in their tracker and still don't care (e.g. lp#1891866). Clearly the better option is to remove packages from distros if they are not maintained anymore. - Ben