At its core, an email blacklist is a type of third party database containing the IP addresses and/or domains of people and organizations with poor email reputations. They're a major component to the SPAM filters built into most email providers. These lists are often updated in real-time, as they help quickly determine whether an email is SPAM (and should thus be filtered away from the user), or whether it is legitimate and can therefore be moved along into someone's inbox.

In this lesson, you will learn more about a number of important topics like:

  • What blacklists actually are.
  • Why ISPs and ESPs use blacklists.
  • How blacklists work.
  • The biggest blacklists you need to be aware of.

How Do Blacklists Work?

If the person you're sending an email to uses an email or Internet Service Provider that employs blacklists, it's important to understand that the IP address of every incoming sender will be checked against the lists in question. If your IP address happens to appear on that list, it will be instantly rejected - meaning that it will never get into the recipient's inbox.

At that point, it will be analyzed by someone's SPAM filter. If it checks out, that message could still make its way into someone's inbox. If it does, it will be sent to the SPAM filter - which is likely its final resting place.

Overall, blacklists are important because email-driven cyber crime like phishing attempts are absolutely on the rise. Therefore, blacklists become an invaluable opportunity for providers to keep their users safe. Likewise, people have less patience for marketing collateral these days and are looking for any opportunity to keep their inboxes less crowded. Blacklists go a long way towards helping them do precisely that.

Of course, all of this makes little difference if you're an email marketer who suddenly finds themselves on an email domain blacklist accidentally.

Overview of the Major Blacklists


Most Internet and email providers use one, or sometimes all, of the following email domain blacklists:

  • Composite Blocking List. This blacklists IP address that display objectively malicious behavior, like spam bots.
  • Spamhaus Block List. This particular list focuses on known spam operations, along with their sources.
  • XBL Exploits Block list. This list is targeted at identifying IP addresses that have been "hijacked."
  • Barracuda. To get on this list, you typically need to have sent SPAM messages directly to a detector powered by the Barracuda Reputation System.
  • SenderScore. This is used by not only email service providers but also corporate email systems, email marketing providers and more.

If you find yourself on an email blacklist as a marketer, it's likely because you've been using the wrong approach to sending a large number of messages to people on your contact list. Sending to large numbers of unverified email addresses, sending an extremely large number of outgoing messages, sending messages that have little to no personalization and using common SPAM words are all things that will likely eventually get you added to one of these lists. This is a big reason why you should only work with email lists that are up-to-date.

How to Tell if You're Blacklisted

The easiest way to check to see if you're on an email blacklist is to enter your IP address or your domain into a site like The Spamhaus Project or SpamCop. This will show you which list you ended up on, along with detailed instructions on how to get yourself removed. The process you'll need to go through for removal will vary depending on the email blacklist, but generally you'll need to submit a formal removal request stating exactly what type of business you run. You'll also need to prove you aren't a spammer.