If it was installed by RPM you can use this shell command (as root) to find out what version you have installed of any program on your box.

Example for squirrelmail:

rpm --query -a | grep squirrelmail

And some others:

rpm --query -a | grep exim

rpm --query -a | grep sendmail

To see the entire list:

rpm --query -a

This isn't 100% because some programs are inside other packages. Like the "net-tools" package contains things like "ifconfig, netstat, route" and others.

For that you could use a command like this:

rpm --query -ai | grep -B 10 -A 10 netstat

Now you can go do some more research on that package via google etc... You can adjust the "-A" and "-B" to a number that shows you what you want, it's how many lines to show (A)fter and (B)efore the keyword.

The Cpanel user control panel has some information on program versions on the left hand side bar.