Hey, imx, here's another idea, recently posted in [SOLVED] Change DSPAM value. I haven't tested it. Maybe you can give it a try.
First I'll give drozzini's patch, then a suggestion of my own.
Locate the line:
and change to:
$spam_score = $dspam_result eq 'Spam' ? 10 : -1; # fabricated
Some discussion of this section of code can be found at [AMaViS-user] [Help] Amavis and header returned to spamassassin - Open Source Archive
$spam_score = $dspam_result eq 'Spam' ? 4 : -2; # fabricated
Looking at the amavisd-new release notes for version 2.6.3, I see a section on configuring the external scanners listed in @spam_scanners. Basically there's a score_factor argument that is multiplied by the DSPAM score to provide a final value. Right now in amavisd.conf.in, the value is 1. To moderate the scores, change it to a smaller value. E.g., edit /opt/zimbra/conf/amavisd.conf.in and change
%%uncomment LOCAL:amavis_dspam_enabled%% mail_body_size_limit => 64000, score_factor => 1
After doing this, restart amavisd with zmamavisdctl restart. What I expect you'll see is that the DSPAM scores will range from -.5 to 5 instead of -1 to 10.
%%uncomment LOCAL:amavis_dspam_enabled%% mail_body_size_limit => 64000, score_factor => .5
Finally, note that the newest release of amavisd-new now passes DSPAM scores to spamassassin. See the release notes for amavisd-new 2.7.0. Zimbra currently ships with amavisd-new 2.6.4, though.