reject_invalid_hostname
#reject_non_fqdn_hostname # These should only be enabled on a true mailhub (even some Debian daemons expect to be able to deliver to localhost)
#reject_non_fqdn_sender
#reject_non_fqdn_recipient
reject_unknown_sender_domain
reject_unknown_recipient_domain
reject_unauth_pipelining
permit_mynetworks
permit_mx_backup
reject_unauth_destination
reject_maps_rbl
reject # Not really needed, but just to be on the safe side...