[CentOS] How current are packages?

I'm relatively new to CentOS. I ordered a VPS and requested CentOS 5.5. As I was installing packages, I noticed that some of the versions are pretty old - for example, Postfix is v 2.3 in the repo (and, according to Postfix's website - no longer mainted). Is this a security risk as the current version is 2.7.1?

Building and compiling Postfix from source seems to cause additional problems with yum, so I'm not sure what to do other than perhaps switch to something like Fedora. Perhaps there's a third-party repo with updated packages that I haven't found?

Thanks,

Matt