I use a combination of multiple RBLs, lowered tag & kill percentages (as OP has already done), modified scores for places that IMHO SpamAssassin is too tolerant, and
penalty-scoring all commercial whitelists. I keep all such modifications in a single file /opt/zimbra/conf/spamassassin/local.cf and I keep that file backed up. That way, when I do an upgrade it's a simple matter of copying local.cf from my backup into the live directory, stop & restart spamassassin and everything stays up.
YMMV, but I've found the following Bayes modifications in local.cf to make my SA scores a lot more effective:
Code:
#My tweaks to the Bayes scoring system - DWM
score BAYES_00 0.0001 0.0001 -6.312 -9.599
score BAYES_05 0.0001 0.0001 -4.110 -6.110
score BAYES_20 0.0001 0.0001 -1.740 -3.740
score BAYES_40 0.0001 0.0001 -0.185 -0.185
score BAYES_50 0.0001 0.0001 0.001 0.001
score BAYES_60 0.0001 0.0001 1.0 1.0
score BAYES_80 0.0001 0.0001 2.5 6.5
score BAYES_95 0.0001 0.0001 7.5 8.5
score BAYES_99 0.0001 0.0001 8.5 9.5