What are the most important blacklists and how do you know if you are listed?

If you are reading this blog, you certainly know what a blacklist is. Nevertheless, we think it’s important to remember their significance in the email world and their impact on your deliverability.

Blacklists are often referred to in different ways: RBL for Real-time Blackhole List or DNSBL for DNS blacklist. These terms all refer to the same thing, a list of IP addresses or domain names that list the mail servers at risk.

When made public, these lists are used by a variety of actors as an indicator of the reputation of an IP address or domain. These actors include any organisation that needs to filter email. These are of course ISPs, system administrators in companies or in the public sector, as well as a whole range of resellers of email filtering solutions.


Two historical blacklists clearly stand out from the rest and are used by most ISPs in the world. These are Spamhaus and Spamcop. If your IP addresses are listed by either of these, you should act very quickly to avoid a lot of your email traffic being blocked.

How do I know if my IP addresses are listed?

» Spamhaus: http://www.spamhaus.org/lookup/
» Spamcop: https://www.spamcop.net/bl.shtml

It is also important to know that these blacklists exchange information. It is not uncommon that after being listed by Spamhaus or Spamcop, your IP addresses are also blocked by dozens of other blacklists.


First of all, there are two main categories of domain name blacklists. The most common are those that analyse the addresses (URIs) of websites cited in spam. The other category is more closely related to referencing all the domain names in emails including, and above all, in the technical header of the email. The best known in this category is again Spamhaus.

The two most important URI blacklists are:

» SURBL: http://www.surbl.org/surbl-analysis
» URIBL: https://admin.uribl.com/


To be removed from a blacklist, it is essential to find out the reasons for the listing and take corrective action before making a delisting request. This step is imperative as most blacklists will ask you to explain why you are on the blacklist in the first place and what corrective actions have been taken that justify delisting.

Once you have found the reason for the listing and have taken steps to prevent it from happening again, you can attempt a delisting request. The procedure is usually explained on the lookup pages (see links above) and consists of filling out a form or sending an email. If your explanation is detailed and justified, your IP or domain name may be quickly removed from the list. On the other hand, if your explanation is imprecise (being precise does not require 10 pages of analysis) or unjustified, you may be refused or asked for clarification.

More information? Please contact us.

Share this

Comments are closed.

There are many more interesting blogs by category for you to read.