In early December I was wrestling with yum and spamassassin trying to get the spamassassin package installed. I remember a yum install didn't work the first time possibly due to some old/broken packages that happened when trying to restore the server from a hard drive failure. Also think I had to update the atomic link. I deleted spamassassin and qmail-scanner and then reinstalled and it seemed to work.
Here's my yum.conf
# cat /etc/yum.conf
[main]
cachedir=/var/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=redhat-release
tolerant=1
exactarch=1
#exclude=kernel* http* sendmail* mysql* qmail* name* bind* php*
#exclude=kernel*,php*
exclude=kernel*, http*, sendmail*, mysql*, qmail*, name*, bind*, php*,perl*
#[base]
#name=Red Hat Linux $releasever - $basearch - Base
#baseurl=http://mirror.dulug.duke.edu/pub/yum-repository/redhat/$releasever/$basearch/
#gpgcheck=1
#[updates]
#name=Red Hat Linux $releasever - Updates
#baseurl=http://mirror.dulug.duke.edu/pub/yum-repository/redhat/updates/$releasever/
#gpgcheck=1
# THIS CHANNEL CONTAINS MY PSA COMPATIBLE RPMS (php, mysql, qmail-scanner, etc)
[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/
[atomic-app-vault]
name=Atomic Rocket Turtle - $releasever - Atomic PSA App Vault RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/app-vault/
[psa-6.0]
name=Atomic Rocket Turtle - $releasever - SW-Soft PSA 6.0 RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/psa-6.0/$releasever/
# baseurl=http://www.atomicrocketturtle.com/atomic/psa-6.0/$releasever/
[psa-7.0]
name=Atomic Rocket Turtle - $releasever - SW-Soft PSA 7.0 RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/psa-7.0/$releasever/
# baseurl=http://www.atomicrocketturtle.com/atomic/psa-7.0/$releasever/
[psa-7.1]
name=Atomic Rocket Turtle - $releasever - SW-Soft PSA 7.1 RPMS
baseurl=http://3es.atomicrocketturtle.com/atomic/psa-7.1/$releasever/
# baseurl=http://www.atomicrocketturtle.com/atomic/psa-7.1/$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/