I can not say if the problem has gone away yet or not. A day or so before updating the server I disabled both spam filtering and virus scanning of e-mail. Since then (or perhaps since the update) we have experienced no slowing.
Since this was an intermittent problem, I have not yet declared it cured. I'll probably wait until Tuesday or Wednesday next week and if no slowing shows up I'll re-enable spam filtering. I'll give that 5 days to a week then, if no slowing occurs, I'll enable virus scanning of e-mails.
I'll try "grep -rl 'Persisten' /etc/e-smith/web | xargs -r rm -f" in the next day or two and see if that cures the other "bug". As root from the command line in ssh?
Thanks
Ted