You can block RBL-listed IP addresses directly in exim rather than
having these mails processed by MailScanner. This will move RBL checking
from MailScanner to exim which should help reduce server load. Emails
from RBL-listed hosts will be completely blocked at exim rather than
tagged as spam and delivered by MailScanner. You should use caution if
you have users on ISPs that tend to get their IP addresses listed in
these RBLs, as their mail will be blocked.
1. Go to WHM »Service Configuration »Exim Configuration Manager > Basic Editor > RBLs. Check your choice of the boxes for RBLs such as bl.spamcop.net or zen.spamhaus.org. Scroll down and click Save.
Watch the output to make sure exim restarted successfully without
errors.
2. Go to WHM > ConfigServer MailScanner FE > MailScanner
Configuration and find the setting "Spam List =". Clear out that field
so it is blank, and click Change.
After doing the above steps you should tail the maillog and
exim_mainlog to ensure that both exim and mailscanner are working
correctly.
tail -f /var/log/exim_mainlog
tail -f /var/log/maillog