включи эти опции:
smtpd_client_restrictions = reject_rbl_client t1.bl.reynolds.net.au
smtpd_client_restrictions = reject_rbl_client bl.spamcop.net
smtpd_client_restrictions = reject_rbl_client list.dsbl.org
smtpd_client_restrictions = reject_rbl_client dnsbl.njabl.org
smtpd_client_restrictions = reject_rbl_client relays.ordb.org
smtpd_client_restrictions = reject_rbl_client ex.dnsbl.org
smtpd_client_restrictions = reject_rbl_client dul.ru
smtpd_client_restrictions = reject_rbl_client dun.dnsrbl.net
smtpd_client_restrictions = reject_rbl_client spam.dnsrbl.net
smtpd_client_restrictions = reject_rbl_client dnsbl.sorbs.net
# Reject the request when the sender mail address has no DNS A or MX record.
# The unknown_address_reject_code parameter specifies the response code for rejected requests (default: 450).
# The response is always 450 in case of a temporary DNS error.
smtpd_client_restrictions = reject_unknown_recipient_domain
# The smtpd_helo_required parameter determines if clients must send a HELO (or EHLO) command
# at the beginning of an SMTP session. Requiring this will stop some UCE software.
smtpd_helo_required = yes
# Reject the request when the hostname in the client HELO (EHLO) command is not in fully-qualified domain form,
# as required by the RFC. non_fqdn_reject_code specifies the response code to rejected requests (default: 504).
smtpd_helo_restrictions = reject_non_fqdn_sender
# Reject the request when the hostname in the client HELO (EHLO) command has no DNS A or MX record.
# The unknown_hostname_reject_code specifies the response code to rejected requests (default: 450).
#
smtpd_helo_restrictions = reject_unknown_hostname
# Reject the request when the client HELO or EHLO parameter has a bad hostname syntax.
# The invalid_hostname_reject_code specifies the response code to rejected requests (default: 501).
smtpd_helo_restrictions = reject_invalid_hostname
спам будет резаться уже на уровне DNS и на стадии коннекта, в отличие от спамассасина, который сначала принимает пиьсмо, а потом уже режет и трафик не экономит.
90% спама режется именно так.