We need to enable sa-update.timer

Makefile

@@ -7,6 +7,7 @@ all: spamassassin-service sa-update-service sa-update-timer
 	@echo "$$SPAMASSASSIN_SERVICE" > /lib/systemd/system/spamassassin.service
 	@echo "$$SA_UPDATE_SERVICE" > /lib/systemd/system/sa-update.service
 	@echo "$$SA_UPDATE_TIMER" > /lib/systemd/system/sa-update.timer
+	systemctl enable sa-update.timer
 	install -d -m700 /etc/mail/spamassassin/sa-update-keys
 	rm -rf Mail-SpamAssassin-3.4.4
 
@@ -78,6 +79,6 @@ OnBootSec=3 min
 OnUnitActiveSec=1 day
 
 [Install]
-WantedBy=spamassassin.service
+WantedBy=timers.target
 endef
 export SA_UPDATE_TIMER