Reboots of the mail server and a restoration from backup did not fix performance issues.

     While there was both a bot-net brute force password guessing attack in progress, which fail2ban found and locked out (over 1200 IPs involved) and an attempt to use the machines name server as an amplifier in a denial of service attack against a third party, (it won’t work because it is rate limited), neither of these represented a significant load or amount of traffic.

     I rebooted the NFS server that holds the mail spool and this fixed the issue.  I do not know what was wrong with it as I was able to access files on the spool directory prior to the boot but it had something to do with file locking as everything was waiting on a lock to clear which never did.