Your theory is not correct. To get more verbose info about bayes classifications, try dropping in a debug.cf (above) and restart amavisd. All mail going through your system will then have additional headers. (Untested; or will amavisd remove them?)
To really debug what's hapening, run spamassassin -D -t. Zimbra installs SpamAssassin in zimbramon/lib/Mail/. Just get the spamassassin script for the same version of SA and use lib '/opt/zimbra/zimbramon/lib';. |