Postfix config help

Hi all,

I started using GPS few days ago and now am observing huge number of triplet.recipient attempts for nonexistent users of my domains. E.g. something@mydomain.com while only my.name@mydomain.com exists. How can I tell Postfix to reject unknown users _before_ greylisting takes place? These emails will be rejected anyway and it's just wasting my resources to do the greylisting before rejecting them?

My current postfix main.cf has this:
smtpd_recipient_restrictions =
permit_mynetworks,
permit_sasl_authenticated,
permit_tls_clientcerts,
check_client_access hash:/etc/postfix/client_access,
reject_unauth_destination,
reject_invalid_hostname,
reject_unknown_recipient_domain,
reject_unauth_pipelining,
check_policy_service unix:private/gps

I believe I need some other reject_ statement but can't find the right one :-(

Thanks!