If you try to use smtpmail-send-it (say by setting your message-send-mail-function to this) and you have a ~/.authinfo file, emacs will give an error about not finding netrc.el. The simplest way to see this is by inspection. Look at /usr/share/emacs/21.4/lisp/mail/smtpmail.el and search for "netrc". I believe the problem here is that smtpmail-cvs-update.patch pulls in a new version of smtpmail.el, which has this dependency, but it fails to pull in netrc.el.
Note that this is only a problem in the Emacs 21 RPM. netrc.el is in the Emacs 22 RPM.
FC6 has reached EOL and this is fixed in the Emacs in F7.