[root@comcwp1 mail]# up2date -i sendmail-cf
Your GPG keyring does not contain the Red Hat, Inc. public key.
Without it, you will be unable to verify that packages Update Agent downloads
are securely signed by Red Hat.

Your Update Agent options specify that you want to use GPG.

To install the key, run the following as root:
     rpm --import /usr/share/rhn/RPM-GPG-KEY