smtpd_helo_required = yes
smtpd_helo_restrictions =
    permit_mynetworks,
    reject_invalid_helo_hostname,
    reject_non_fqdn_helo_hostname,
    warn_if_reject reject_unknown_helo_hostname,
    check_helo_access hash:/etc/postfix/access_helo,
    reject_rhsbl_helo multi.surbl.org
smtpd_client_restrictions = permit_mynetworks,
    warn_if_reject reject_unknown_client,
    check_client_access hash:/etc/postfix/access_clientip,
    reject_rbl_client sbl-xbl.spamhaus.org,
    reject_rbl_client list.dsbl.org