The Spamassassin config in Zimbra has a very high default score for bayes matching of 99, 95, 90, etc, percent. A mail with subject and body “test” or “asdfaewf a” is often marked as 99% bayes, even though the spamfilter has seen no training mail. This is absurd.
To amend this, I put this in /opt/zimbra/conf/spamassassin/local.cf:
score BAYES_99 2.500 score BAYES_95 2.000 score BAYES_90 1.500 score BAYES_85 1.000 score BAYES_80 0.500