[CentOS] Updating - CentOS Repository

Hello, I was wondering if any of you know why the CentOS repository are not updated? for example, i just heard about the bugs of the version <=1.4.4 of Squirrelmail and on their website there is already a stable packet 1.4.5, but in the CentOS repository the only available version is the 1.4.3 9a

Any ideas?

Another thing, im new using yum so i have a question, for example if i put "yum install squirrelmail1.4.5" but i have the version 1.4.3 already installed in my system, what happens? does the yum override the old version? what happens with the config files?