Can you copy/paste the output of the running that command here?
Also see your other post I just replied to...
Yum will do a number of things, it will check the repositories, download headers, show you a list of what it is about to do and ask for confirmation from you.
Once you give confirmation to go ahead, it will then install the spamassassin (and any dependencies needed). The stuff it prints out while it is running is fairly explanatory, hopefully you saved that info, please post it here.
Also post the contents of /var/log/yum.log (not a direct replacement for posting the command line output). The log file is just a summary, not as detailed as the command line output.
Let's quit this thread and just use your other post.... too confusing with multiple posts