Open the file /etc/yum.conf and replace any repos there with:
[atomic]
name=Atomic Rocket Turtle - $releasever - Atomic PSA-Compatible RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/art/$releasever/
baseurl=http://www.atomicrocketturtle.com/atomic/art/$releasever/
[psa-7.5]
name=Atomic Rocket Turtle - $releasever - SW-Soft PSA 7.5 RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/psa-7.5/$releasever/
baseurl=http://www.atomicrocketturtle.com/atomic/psa-7.5/$releasever/
[base]
name=Atomic Rocket Turtle - $releasever - Base OS RPMS mirror
baseurl=http://3es.atomicrocketturtle.com/3rd-party/base/$releasever/
[updates]
name=Atomic Rocket Turtle - $releasever - OS Update RPMS mirror
baseurl=http://3es.atomicrocketturtle.com/3rd-party/updates/$releasever/
Then from the command line:
#rpm --import
http://www.atomicrocketturtle.com/RPM-GPG-KEY.art.txt
#yum install clamav spamassassin qmail-scanner
Once they are done, run
#/usr/bin/qmail-scanner-reconfigure
That should about do it.