Sorry for late reply, too busy lately.
But i've never used syslog daemons on the CentOS boxes, but seen the mail log go to /var/log/maillog, but now there is no file in there at all. Yes, restarted qmail as well as server.
Update: got it working after installing syslog.
Thanks a lot @chrisf
Restart the syslog, restart qmail.
Did you try to reboot the server? That is always last option for me, but sometimes it works.