The Scalix installer creates S02scalix-tomcat and S02scalix-postgres in /etc/rc.d/rc3.d & /etc/rc.d/rc5.d.
Unfortunately, postgres will fail to start unless networking is already started. Networking is started as S05network. Therefore, scalix-postgresql will never start successfully.
Renaming the scripts to S07scalix-tomcat and S07scalix-postgres resolves the problem.
I'll have a look at Red Hat when I'm in front of one of their boxes next. I put this here rather than in Installation because most people won't notice it until after they reboot their box.