En mi opinión, si no ha cambiado, no vale la pena.
https://listas.es.freebsd.org/pipermail/freebsd/2007-June/013191.html
https://forum.pfsense.org/index.php?topic=3540.0
Hasta que no migré mi PostFix a Google Apps For Education utilicé DNSBL (http://en.wikipedia.org/wiki/DNSBL) con bastante efectividad.
Algo así en main.cf
smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_rbl_client zen.spamhaus.org, reject_rbl_client bl.spamcop.net
pfSense tiene un paquete PostFix que debe hacer esto.
Postfix Forwarder 2.10.2 pkg v.2.3.7
Postfix mail forwarder acts as a relay server for your domain.
It can do first and second line antispam combat before sending incoming mail to local mail servers.
Postfix can also detect zombies, check RBLS, SPF, seach ldap for valid recipients and use third part antispam engines like policyd and mailscanner for better antispam solution.