iredmail-doc/howto/enable.dnsbl.md

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# Enable DNSBL service in Postfix to reduce spam
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.
## References
* [Postfix Configuration Parameters: reject_rbl_client](http://www.postfix.org/postconf.5.html#reject_rbl_client)
* [Spamhaus website](http://www.spamhaus.org)
* [Spamhaus DNSBL Usage Terms](https://www.spamhaus.org/organization/dnsblusage/)