33 lines
1.3 KiB
Markdown
33 lines
1.3 KiB
Markdown
# Enable DNSBL service in Postfix to reduce spam
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> Important note: if you're running a high-traffic mail server, you'd better
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> setup a local DNS server to cache DNS queries, because free RBL services
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> like zen.spamhaus.org may improperly reply if your server exceed the
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> DNS query limit. Also, mail service higly relies on DNS queries, so a local
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> DNS server speeds up the mail flow.
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You can enable additional DNSBL services in Postfix to reduce spam. We use
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`zen.spamhaus.org` for example below.
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* Open Postfix config file `/etc/postfix/main.cf` or
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`/usr/local/etc/postfix/main.cf` (on FreeBSD), append
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`reject_rbl_client zen.spamhaus.org` to parameter `smtpd_recipient_restrictions`.
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Final setting looks like below:
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```
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smtpd_recipient_restrictions = ..., reject_unauth_destination, reject_rbl_client zen.spamhaus.org
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```
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It must be placed after `reject_unauth_destination`. You can add more DNSBL
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services after `reject_unauth_destination`, and they will be queried in the
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specified order.
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* Restart or reload Postfix service is required.
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## References
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* [Postfix Configuration Parameters: reject_rbl_client](http://www.postfix.org/postconf.5.html#reject_rbl_client)
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* [Spamhaus website](http://www.spamhaus.org)
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* [Spamhaus DNSBL Usage Terms](https://www.spamhaus.org/organization/dnsblusage/)
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