is there any other ways to reduce the spam emails except the following:

enabled greylisting

changed the SPAM score in /etc/amavisd/amavisd.conf

from default:

$sa_tag_level_deflt  = 2.0;  # add spam info headers if at, or above that level
$sa_tag2_level_deflt = 6.2;  # add 'spam detected' headers at that level     
$sa_kill_level_deflt = 6.9;  # triggers spam evasive actions (e.g. blocks mail)

to:

$sa_tag_level_deflt  = 2.0;  # add spam info headers if at, or above that level
$sa_tag2_level_deflt = 2.8;  # add 'spam detected' headers at that level     
$sa_kill_level_deflt = 2.8;  # triggers spam evasive actions (e.g. blocks mail)

still getting around 10 emails in one day ...

Thank You