OS : CentOS 5.6 64bit
ZCS : Release 7.1.0_GA_3140.RHEL5_64_20110329150833 CentOS5_64 FOSS edition.

[root@mail conf]# su zimbra
[zimbra@mail conf]$ vi /opt/zimbra/conf/postfix_recipient_restrictions.cf

Add line 6 (highlight line) to postfix_recipient_restrictions.cf file

%%contains VAR:zimbraServiceEnabled cbpolicyd, check_policy_service inet:127.0.0.1:10031%%
reject_non_fqdn_recipient
permit_sasl_authenticated
permit_mynetworks
reject_unauth_destination
check_client_access hash:/opt/zimbra/conf/allow_rbl
reject_unlisted_recipient
%%contains VAR:zimbraMtaRestriction reject_invalid_hostname%%
%%contains VAR:zimbraMtaRestriction reject_non_fqdn_hostname%%
%%contains VAR:zimbraMtaRestriction reject_non_fqdn_sender%%
%%contains VAR:zimbraMtaRestriction reject_unknown_client%%
%%contains VAR:zimbraMtaRestriction reject_unknown_hostname%%
%%contains VAR:zimbraMtaRestriction reject_unknown_sender_domain%%
%%explode reject_rbl_client VAR:zimbraMtaRestrictionRBLs%%
%%contains VAR:zimbraMtaRestriction check_policy_service unix:private/policy%%
permit

Create file allow_rbl in /opt/zimbra/conf

[zimbra@mail conf]$ vi /opt/zimbra/conf/allow_rbl

allow_rbl file inside :

114.57.xxx.xxx OK
202.155.xxx.xxx OK

Convert the allow_rbl file into maptype database file and restart MTA

[zimbra@mail conf]$ postmap /opt/zimbra/conf/allow_rbl
[zimbra@mail conf]$ zmmtactl restart
Rewriting configuration files...done.
postfix/postfix-script: refreshing the Postfix mail system
Stopping saslauthd...done.
Starting saslauthd...done.
[zimbra@mail conf]$