Hi Klug. Thanks for responding. I looked at that thread, and there was some good information in it. The bug that was filed as a result of that thread appears to be resolved -- or at least that's the status of the bug in Zimbra's bug tracker.
I thought perhaps updating to 4.0.3 would fix the problem, since the bug was filed against 4.0.2, but no such luck. The problem persists after upgrading to 4.0.3, so I assume the bug was fixed in a yet-to-be-released version.
So, following are how I fixed these errors, based on the information in the aforementioned thread. To fix the "cannot open bayes databases" errors, the following command did the trick:
$ sudo rm /opt/zimbra/amavisd/.spamassassin/bayes_*
To fix the "config: could not find the site rules directory" problem:
$ sudo mkdir /etc/mail
$ sudo ln -s /opt/zimbra/conf/spamassassin /etc/mail/spamassassin
And lo and behold, these two changes appear to have addressed all of the problems I reported in my original message, at least via manual zmtrainsa commands. Both SpamAssassin and DSpam appear to be -- for the first time -- actually learning from the messages in the spam/ham training accounts.
Tip for initial ham training:
As I mentioned in my original message, I don't recall setting passwords for the training accounts. From the Zimbra Admin interface, you can however click on each of them and then click the "Change Password" button to give them passwords. This allowed me to mount the ham training account via IMAP, drag over a ton of messages into its inbox, and run the zmtrainsa command:
zmtrainsa mail.mydomain.com trainham@mydomain.com myacctpw ham
Question #1: Will my "re-setting" (assuming they were ever set in the first place) of the training account passwords cause a problem for the nightly training cron jobs?
Question #2: Some messages arrive with no DSpam headers whatsoever. What circumstances would cause this?
Question #3: Could we possibly get a timestamp at the beginning of a given night's batch in spamtrain.log?
Looking forward to your thoughts. Thanks for listening!
Justin