SORBS and other RBLs we use block legitimate emails on occasion, although the ones being blocked are from legitimately blacklisted freemail servers (googles, yahoos, etc).

My main question here is, is the postfix_rbl_override only for domains, or can individual addresses be listed here as well?
example
yahoo.com OK <-- This works for us
example@yahoo.com OK <-- Does not seem to be working for us

When I get notified of these addresses I add them to both RBLs and SpamAssassin whitelists
/opt/zimbra/conf/postfix_rbl_override
/opt/zimbra/conf/salocal.cf.in

Here is my /conf/zmconfigd/smtpd_recipient_restrictions.cf

%%contains VAR:zimbraServiceEnabled cbpolicyd, check_policy_service inet:localhost:@@cbpolicyd_bind_po
rt@@%%
reject_non_fqdn_recipient
check_client_access hash:/opt/zimbra/conf/postfix_rbl_override
reject_unlisted_recipient
%%contains VAR:zimbraMtaRestriction reject_invalid_helo_hostname%%
%%contains VAR:zimbraMtaRestriction reject_non_fqdn_helo_hostname%%
%%contains VAR:zimbraMtaRestriction reject_non_fqdn_sender%%
%%contains VAR:zimbraMtaRestriction reject_unknown_client_hostname%%
%%contains VAR:zimbraMtaRestriction reject_unknown_helo_hostname%%
%%contains VAR:zimbraMtaRestriction reject_unknown_sender_domain%%
%%explode reject_rbl_client VAR:zimbraMtaRestrictionRBLs%%
%%contains VAR:zimbraMtaRestriction check_policy_service unixrivate/policy%%
permit

I then run ...
postmap /opt/zimbra/conf/postfix_rbl_override
zmamavisdctl restart & zmmtactl restart

Thank you for your help!