Not all the best DNS blocklists are created equal

Find out which blocklists to pay attention to, and how to keep them from trapping your email program. Read more...



The word “blocklist” can almost seem like something out of a movie—a little dramatic, a little silly, and a little bit unreal. Unfortunately, in the real world, blocklists are definitely something you need to be mindful of… especially when it comes to your email program. In this post, we’ll tell you a little more about blocklists and how to avoid their drama.

What is a blocklist anyway?

Before we run through the different types of email blocklists, let’s cover what blocklists are. DNSBL (DNS-Based Blocklists) and RBL (Real-time Blocklists) are lists of IP addresses that are suspected of sending spam and are used to prevent unwanted email messages from reaching unsuspecting recipients. DNS-based blocklists (Domain Name System-Based Blockllists) are based, as the name suggests, on their listed IP addresses’ domain names. RBL (real-time blocklists) are based on IP addresses that are caught in real-time. Simple, right?

Why was the DNS blocklist server list created?

The DNS blocklist server list was created to help stop the flood of spam that began when widespread usage of email became popular. Because of its creation, email providers could have a resource to see which IP addresses had a reputation for sending unwanted or malicious email to recipients. They could use this list (and later, other lists like the RBL list) to take effective action against spammers without harming normal ISPs.An important thing to note is that blocklists don’t actually block your messages—the actual email providers do.

These providers use this information from various blocklist services along with internal metrics to make decisions on whether or not to block a message. This is noteworthy because just being listed on a random blocklist isn’t necessarily going to cause you problems with your email deliverability. However, if you hit these email providers’ metrics and show up on some more reputable blocklists, well… let’s just say that the curtain could start to close on your email program. So, how do you avoid being put on a blocklist?

How do you avoid being put on a blocklist?

A word of caution: even if being put on a certain blocklist seems inconsequential or unimportant, the fact remains that something in your email program caused your blocklisting to happen in the first place. As a result, you should always be maintaining best practices when it comes to your email program. Oftentimes, blocklists happen because you send a message to a spam trap that is being monitored by one of these blocklist operators.

If you do happen to get listed, take a close look at your email list collection practices. Make sure you are incorporating some form of confirmed opt-in or email validation into your sign-up process. Email validation can help weed out bad emails and ensure that you’re sending to real, interested consumers. Additionally, always keep up with your email list hygiene. You might also want to check how you’re sending, like from a shared server versus your own SMTP. Once you’ve done the work to identify the cause of a listing, feel free to put in a blocklist removal request. If you don’t take necessary measures to prevent a re-listing, you will get listed again, guaranteed. Frequent recurrences could lead to future removal requests being rejected, so fix the problem as soon as possible before you’re listed again. Plus, your email service provider will be happy to see you off of the blocklist for good, so everyone wins.

Which blocklists matter?

There are a lot of blocklists out there, and we mean a lot: check here to see how many we are talking about. These are created by large, reputable businesses, as well as lesser-known companies, and sometimes fraudsters. Since pretty much anyone can create a blocklist, they aren’t all treated the same by email providers—and you should focus on paying attention to the ones that matter most.So how do you decipher between the reputable blocklists and the fraudsters? Don’t fret. We’ve got you covered with a list of some of the most reputable… well, lists, and these are the ones we pay the most attention to:

Wrap up

And that’s a wrap on blocklists. They’re pretty simple as a concept, but not employing email best practices can leave you open to being put on one or more of them. Mailgun has a variety of services that help boost your deliverability and reputation and prevent blocklisting, like the aforementioned email validation, SMTP relay, and more. The important thing is that, however you choose to use your email program, you make sure you’re avoiding blocklists and staying above the drama.

Learn about our Deliverability Services

Deliverability Services

Looking to send a high volume of emails? Our email experts can supercharge your email performance. See how we've helped companies like Lyft, Shopify, Github increase their email delivery rates to an average of 97%.

Related readings

FML, I'm on an email blocklist. What do I do?

Getting blacklisted happens to a fair number of email marketers, and it sucks. But it isn't the end of the world. Read more...

Read more

Troubleshooting email soft bounces

Email soft bounces can have a negative impact on your deliverability. Discover what they are and how to fix them.

Read more

The basics of SPF records

What are SPF records, and how can you use them to benefit your email program?

Read more

Popular posts

Mailgun iconSee what you can accomplish with the world's best email delivery platform. It's easy to get started.Let's get sending
CTA icon Mailgun Icon