“DNS Blackhole Lists in Plesk”- The way we used it to prevent spam

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Every day, a lot of people use email. It’s one of the keys for quick and easy communication.

Unfortunately, junk mail, more commonly known as spamis one of the big problems of the email.

With hundreds of spam in your inbox, you can lose the important email.

That’s why, we often get requests from our clients to prevent spam on the server as part of our Server Management Services.

Today, we’ll see how our Support Team prevent spam by setting up “DNS Blackhole Lists in Plesk”.



Knowing more on DNS Blackhole List in detail…

First, let’s understand further on DNS Blacklists.

DNS Blacklists or DNS Blackhole Lists (DNSBL) is a service that contains a set of IP Addresses that are involved in Spam activities.

Nowadays, most of the mail servers have configured to reject or flag messages when sent from an IP listed in DNS Blackhole Lists.

Plesk provides many methods for spam protection. It includes features like

  1. Setting a strong password when creating an email account.
  2. Limit the size of email coming to the server.
  3. Use SMTP authentication when configuring the email client.
  4. Enable DomainKeys or SPF (Sender Policy Framework).

However, many servers still face spam problems. That’s where DNS Blackhole Lists (DNSBL) has a major role to play. This is one of the options that our Dedicated Engineers recommend to customers with Plesk servers.


Setting up DNS Blackhole Lists in Plesk

Recently, our customer approached us with the problem like “they are getting a lot of spam emails” in their inbox. Customer had setup Plesk control panel in his server.

Even though they had configured SpamAssassin in Plesk, they were getting a lot of spam emails in the user’s mailbox.

Let’s see how our Support Engineers used DNS Blackhole Lists in Plesk to prevent spam on the server.

1. The very first step we did was to check the logs, to verify if they were really receiving any junk emails.

2. We found that there were suspicious emails. We could see that many mails originated from bad IP addresses. That’s why, we decided to enable Blackhole lists on the server. We performed the following steps to enable DNS Blackhole Lists.

  • In Plesk > Go to Tools & Settings > Mail Server Settings (in the Mail group).
  • Select the Switch on spam protection based on DNS blackhole lists check box.
  • In the DNS zones for DNSBL service input box, enter “sbl.spamhaus.org;xbl.spamhaus.org” into DNS zones for DNSBL service.

  • We set the blacklists as: –
  • Click OK.

With that DNS Blackhole Lists was enabled on the server. Then, the logs started showing errors like 550 (connection refused). Thus, it denied the messages from black listed IP addresses.


Related errors when setting DNS Blackhole Lists.

From our experience in fixing the issues with DNS Blackhole Lists, the following are some of the related errors our Support Team found so far.

1.Misspelled DNSBL

This error happens when you incorrectly type the entry in DNS zone for DNSBL service. It results in “This is not the DNSBL you’re looking for” error.


2. Running outdated SpamAssassin

Often outdated SpamAssasin create problems with DNS Blackhole Lists. Your SpamAssassin version should be upgraded if it’s an old version, only then it queries DNS zone entry listed in DNS Blackhole Lists.


3. DNSBL blocks nothing

There can be cases where the Blackhole lists do not block any mail on the server. This happens when there are problem with DNS resolvers on the server.

To fix it, our Dedicated Engineers add Google Public DNS ( in the resolvers list.

[Trouble with DNS Blackhole Lists? Our Plesk Engineers can fix it for you now.]



To be more precise, “DNS Blackhole Lists” is a powerful tool to avoid spam activities like junk and malicious emails. Today, we saw how our Technical Team set up “DNS Blackhole Lists in Plesk” to fight against Spam.

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