not sure whether or not this is possible, but i've been trying to incorporate greylisting into zimbra using postgrey which relies on adding options to the smtpd_recipient_restrictions value in main.cf (check_policy_service inet:127.0.0.1:10023)

problem is that it appears the main.cf is overwritten when zimbra is started... is there a proper way to do this? (or an inproper way that works )

thanks!