I have upgrade to Leap 15.4 to find my dkimproxy setup broken. I noticed the
following things:

1. there was one dkimproxy service, now there are two dkimproxy-in and
dkimproxy-out. The new services are disabled even though the old one was
enabled
2. The dkimproxy_in.service file references  the /run/sysconfig/dkimproxy
environment file
2a. The dkimproxy_env.sh script is supposed to create that file, but
/run/sysconfig is not created at all to that script fails
2b. The dkimproxy_env.sh sets "HFQHN=$( hostname -f )" dkimproxy-in.service
uses --hostname=${FQHN}

While problem 1 is a one-time fix, the problems from 2 are more persistent and
are ideally solved in the package.

Note: systemd integration was contributed in bug #1116007