A few parts of the configuration can be changed, however the recommended way
is to add the reject_rbl_client keyword to the smtpd_client_restritions
configuration parameter:
In your main.cf file (usually /etc/postfix/main.cf) set the following:
smtpd_client_restrictions = reject_rbl_client dnsbl.sorbs.net - where 'dnsbl.sorbs.net' is the SORBS zone you wish to use.
Note: the 'reject_rbl_client' restriction should be added rather than replacing
the current options.
