#anti-spam...
disable_vrfy_command = yes
smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_helo_restrictions =
    permit_mynetworks,
    reject_non_fqdn_helo_hostname,
    reject_invalid_helo_hostname,
    warn_if_reject reject_unknown_helo_hostname,
    permit
smtpd_recipient_restrictions =
    permit_mynetworks,
    reject_invalid_hostname,
    reject_non_fqdn_hostname,
    reject_non_fqdn_sender,
    reject_non_fqdn_recipient,
    reject_unknown_sender_domain,
    reject_unknown_recipient_domain,
    reject_unauth_pipelining,
    reject_unauth_destination,
    reject_rbl_client zen.spamhaus.org,
    reject_rbl_client bl.spamcop.net,
    reject_rbl_client dnsbl.dronebl.org,
    permit
smtpd_client_restrictions =
    permit_mynetworks,
    reject_rbl_client psbl.surriel.com,
    permit
smtpd_data_restrictions =
    permit_mynetworks,
    reject_unauth_pipelining,
    permit