Привожу выдержки из настроек в main.cf для фильтрации спама в версии Postfix
2.2 его собственными силами.
Использую также SASL2 для аутентификации (это не обязательно) и PCRE (аналог regexp).

/etc/postfix/main.cf

====================
   disable_vrfy_command = yes
   strict_rfc821_envelopes = yes
   smtpd_etrn_restriction = reject
   smtpd_sasl_auth_enable = yes
   smtpd_helo_required = yes
   smtpd_helo_restrictions =

   smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_non_fqdn_recipient,
        check_recipient_access pcre:/etc/postfix/recipient_checks.pcre,
        reject_unknown_recipient_domain,
        reject_unverified_recipient,
        reject_unauth_destination,
        reject_unauth_pipelining,
        permit_auth_destination

   smtpd_data_restrictions =
        reject_unauth_pipelining,
        reject_multi_recipient_bounce,
        permit

   smtpd_delay_reject=no

   # здесь у меня пусто, но можно ввести свой контроль
   smtpd_client_restrictions =
   #       check_client_access hash:/etc/postfix/maps/access_client

   # количество RBL серверов регулируйте сами, я дал наиболее распространённые, на мой взгляд
   smtpd_sender_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_invalid_hostname,
        reject_non_fqdn_hostname,
        reject_non_fqdn_sender,
        check_sender_access hash:/etc/postfix/maps/ not_our_domain_as_sender,
        reject_unknown_client,
        reject_unknown_sender_domain,
        reject_unknown_hostname,
        check_client_access pcre:/etc/postfix/client_checks.pcre,
        check_helo_access pcre:/etc/postfix/helo_checks.pcre,
        reject_rbl_client bl.spamcop.net,
        reject_rbl_client sbl-xbl.spamhaus.org,
        reject_rbl_client dul.dnsbl.sorbs.net,
        reject_rbl_client list.dsbl.org,
        reject_rbl_client dnsbl.njabl.org,
        reject_rbl_client relays.ordb.org,
        reject_rbl_client cbl.abuseat.org,
        reject_rbl_client opm.blitzed.org,
        reject_rbl_client dul.ru,
        reject_rhsbl_sender dsn.rfc-ignorant.org
====================

/etc/postfix/client_checks.pcre

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   /(modem|dia(l|lup)|cp[ce]|dsl|p[cp]p|cable|catv|poo(l|les)|pppoe|dhcp|client|
   customer|user|host|[0-9]{4,})(-|_|\.|[0-9])/ REJECT Invalid hostname (client)

   /[0-9]+-[0-9]+/                 REJECT Invalid hostname (D-D)
====================

/etc/postfix/helo_checks.pcre

====================
   /[^[] *[0-9]+((\.|-|_)[0-9]+){3}/ REJECT Invalid hostname (ipable)

   /(modem|dia(l|lup)|cp[ce]|dsl|p[cp]p|cable|catv|poo(l|les)|pppoe|dhcp|client|
   customer|user|host|[0-9]{4,})(-|_|\.|[0-9])/ REJECT Invalid hostname (client)

   /[0-9]+-[0-9]+/                 REJECT Invalid hostname (D-D)
====================


/etc/postfix/recipient_checks.pcre

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   /[@!%].*[@!%]/ 550 Please use user@domain address forms only.
====================

/etc/postfix/maps/not_our_domain_as_sender

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   yourdomain.tld     554 Go away, bloody spammer!
====================