Ah yes, thank you very much, i think i got it this time, here's the config output
from postfix conf
#su - zimbra -c 'postconf | grep smtpd_recipient_restrictions'
smtpd_recipient_restrictions = reject_non_fqdn_recipient, permit_sasl_authenticated, permit_mynetworks, reject_unlisted_recipient, reject_rbl_client zen.spamhaus.org, reject_invalid_hostname, reject_non_fqdn_hostname, reject_non_fqdn_sender, reject_unauth_destination, permit
Saw some mails being "blocked using zen.spamhaus.org;" instantly and am receiving testing mails from gmail, so it appears its working. Time will tell, will keep an eye on the logs for a while.
# su - zimbra -c 'zmprov gacf | grep zimbraMtaRestriction'
Thanks for support, guys.