Well I upgraded the server to Fedora 10 and in the upgrade process chkconfig shutdown sendmail. Everything looked OK until I sent out the community bulletin. Thousands of messages were queued up in /var/spool/clientmqueue/. When sendmail was restarted it would try to resend these messages every hour on the hour. This would cripple the server while spamassassin tried to keep up. At first the problem would last for a few minutes, but then it would take a little longer every hour.
I deleted all the files and restarted sendmail and spamassassin. It looks OK and I am resending the community bulletin to let members know we're all OK again.