After the upgrade from 12.3 I found out that spmad was not running anymore.
When trying to start it manually I get:

# /etc/init.d/spamd restart
redirecting to systemctl restart spamd.service
Job for spamd.service failed. See "systemctl status spamd.service" and
"journalctl -xn" for details.

Running the latter command yields:

Dec 29 16:40:11 linux-wulv echo[6901]: Starting spamd:
Dec 29 16:40:11 linux-wulv spamd[6903]: logger: removing stderr method
Dec 29 16:40:11 linux-wulv spamd[6905]: config: no rules were found! Do you
need to run 'sa-update'?
Dec 29 16:40:12 linux-wulv spamd[6903]: child process [6905] exited or timed
out without signaling production of a PID file: exit 255 at /us
Dec 29 16:40:12 linux-wulv spamd[6903]: child process [6905] exited or timed
out without signaling production of a PID file: exit 255 at /us
Dec 29 16:40:12 linux-wulv systemd[1]: Failed to start Daemonized version of
spamassassin.
-- Subject: Unit spamd.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit spamd.service has failed.
-- 
-- The result is failed.

# rpm -q perl-Mail-SpamAssassin
perl-Mail-SpamAssassin-3.4.0-44.1.3.x86_64
# rpm -q spamassassin
spamassassin-3.4.0-44.1.3.x86_64

Solution:
Running sa-update manually makes spamd start with '/etc/init.d/spamd restart'.