main.cf:
smtpd_client_restrictions =
    permit_mynetworks,
    reject_unknown_client,
    reject_rbl_client sbl.spamhaus.org,
    reject_rbl_client bl.spamcop.net,
    reject_rbl_client relays.ordb.org,
    check_client_access hash:/etc/postfix/access


/etc/postfix/access:
.ru     REJECT no spam