Enable DNSBL service in Postfix to reduce spam

Important note: if you're running a high-traffic mail server, you'd better setup a local DNS server to cache DNS queries, because free RBL services like zen.spamhaus.org may improperly reply if your server exceed the DNS query limit. Also, mail service higly relies on DNS queries, so a local DNS server speeds up the mail flow.

You can enable additional DNSBL services in Postfix to reduce spam. We use zen.spamhaus.org for example below.

Open Postfix config file /etc/postfix/main.cf or /usr/local/etc/postfix/main.cf (on FreeBSD), append reject_rbl_client zen.spamhaus.org to parameter smtpd_recipient_restrictions. Final setting looks like below:

smtpd_recipient_restrictions =
    ...
    reject_unauth_destination
    reject_rbl_client zen.spamhaus.org

It must be placed after reject_unauth_destination. You can add more DNSBL services after reject_unauth_destination, and they will be queried in the specified order.

Restart or reload Postfix service is required.

Another popular DNSBL server

Another popular DNSBL server address is b.barracudacentral.org. For more details, please read its web site: Barracuda Reputation Block List (BRBL)

References

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Enable DNSBL service in Postfix to reduce spam

See also

References