How to avoid landing in an email blocklist: Best practices

“Oh no, I’m on a blocklist. But why? I don’t send out spam!” There’s more than one way to climb a mountain, and more than one way to end up on a blocklist. Don’t worry, we’ve got you covered. In this article, we’ll go over what email blocklists are, how to delist your domain name from them, and how to avoid getting on them in the first place.



We can’t think of many things more immediately impactful to your deliverability than landing on a blocklist. Once you’ve been flagged, ISPs won’t let you through the gate into the inbox, and that hurts everything from your engagement to your bottom line.

Let’s jump right into it.

What is email blocklisting?

A blocklist is a list of IP addresses or domain names that get flagged as sources of suspicious behavior, malicious content, or spam messages. There are many lists, but some pack more of a punch in terms of affecting your deliverability and sender reputation. Some popular blocklists include:

  • Spamhaus

  • MXToolBox

  • Barracuda Reputation Block List (BRBL)

  • Spamcop


  • Google Transparency Report

  • PhishTank

The term "email blocklist" was originally called "email blacklist." However, the email industry has transitioned to the term "email blocklist," and we have updated this post to reflect the change.

What happens when a domain is blocklisted?

Email clients and email service providers (ESPs) may work to prevent emails from blocklisted domains from reaching their email servers. If your domain becomes blocklisted, your emails probably won’t reach your subscribers. In a nutshell, landing on a blocklist impacts your email deliverability and your sender reputation. If your messages do get through, they’ll most likely end up in the spam folder, not the inbox. In addition, some internet service providers (ISPs) restrict access to blocklisted IPs and domains.

What are 4 reasons why I might have been blocklisted?

So you’ve been blocklisted. Don’t worry – this isn’t the end of the world. We’ll go over how you can avoid getting blocklisted in the first place or how you can get delisted later on. But first, here are four common reasons you might been blocklisted:

  • You’re suddenly sending out a large volume of emails

  • Your content looks spammy

  • Your account was hacked

  • Your subscribers have been marking your email messages as spam

Let’s take a closer look at each of these below.

Why is a sudden large volume of emails a red flag?

Spammers often suddenly ramp up in volume. Blocklist vendors might see a sudden increase in your email volume as a red flag indicating that you’re sending out spam instead of legitimate emails. Avoid this by batching your emails or using email list segmentation to break up large mailing lists.

How can I avoid spammy-looking content?

Your content might not be spam, but it’ll get flagged by blocklists if it looks like spam. While there are no set rules for exactly what spammy content looks like, here are some things to tips to avoid looking spammy:

  • Don’t use ALL CAPS

  • Don’t use poorly formatted HTML

  • Don’t use all image emails

  • Don’t use lots of exclamation points.

Can I end up on a blocklist if my account is compromised?

If you’ve been exposed to a cybersecurity threat, the hacker might commandeer your account to send out spam. Not only does this ruin your sender reputation, but it might also land you on a blocklist. Implement good cybersecurity practices and use two-factor authentication (2FA) to guard against these threats.

Is it bad that my subscribers mark my emails as spam?

Yes. This is bad. Very bad. If your subscribers can’t see a clear way to unsubscribe, they might mark your emails as spam. Too many spam complaints will land you on the blocklist.

How can I know if I’ve been blocklisted?

Not sure if you’ve actually been blocklisted? Your ISP should signal whether any of your IP addresses or domain names are on an email blocklist, but sometimes things slip through the cracks. In this case, you can run a domain blocklist check on your email to see if your domain is on a blocklist.

To do this, run your domains manually through individual blocklists. Alternatively, you can save time by using a tool that runs your email against major blocklists. Check out Mailgun’s Blocklist Check Tool to see if your domains are on any blocklists. With this information, you can go back to the individual blocklists to see why your emails are getting flagged.

Blocklists and spam traps monitoring tools

The good news about blocklists is that there are a few major ones that are impactful, like Spamhaus or Barracuda, and others that can be publicly referenced. The downside is that these lists will never seek out a domain to alert them of a blocked status.

This is where blocklist monitoring comes in, and why it’s important to use tools that have curated an extensive library of blocklists to validate your domain against.

Spam Trap and Blocklist Monitoring from Mailgun Optimize provides insight into how often you are sending to pristine, recycled, and typo spam traps, and automates triggered notifications when your IP shows up on major blocklists. Identify issues in near-real-time so you can protect your sender reputation and avoid serious disruption to your email program.

What are some best practices to avoid landing on an email blocklist?

The best course of action is preventative action. After all, blocklists just spell disaster for email open rates, conversions, and ROI. Keep your marketers happy by minimizing deliverability problems!

Take a look at our list of best practices so you can avoid landing on an email blocklist:

Let’s dive into each of these in more detail below.

How can I maintain a healthy subscriber list?

Keep a healthy subscriber list by staying up-to-date with your mailing list. Remove unengaged users or email addresses that have bounced more than two times in a given time frame. Most importantly, before sending, be sure to verify your email addresses. Stop the problem before it happens!

Monitor for blocklists and spam traps with Mailgun Optimize

How can I maintain a healthy subscriber list?

Keep a healthy subscriber list by staying up-to-date with your mailing list. Remove unengaged users or email addresses that have bounced more than two times in a given time frame. Most importantly, before sending, be sure to verify your email addresses. Stop the problem before it happens!

Why is it important to have clear opt-in and opt-out options?

Clear opt-in and opt-out options will save you a lot of headaches when it comes to invalid email addresses or spambots. For instance, double opt-in requires users to submit their email addresses in a web form and then open an email to confirm their email address and interest in your mailing list. Double opt-ins check whether or not a subscriber intended to sign up for a mailing list and whether they’ve input their emails correctly.

Having a clear opt-out or unsubscribe option is just as important as having a clear opt-in option. If your subscribers can’t find a clear opt-out button, they might just mark your emails as spam and call it a day. They might not think anything more of it, but enough of these spam complaints could land your domain on a blocklist.

What email authentication protocols do I need?

We go into email authentication protocols in detail elsewhere, but let’s go over the basics again. You’ll need to set up the following protocols:

  • Sender Policy Framework (SPF): SPF uses a Domain Name System (DNS) record to identify which email sources are valid for a given domain. You need to set up your SPF to indicate which IP addresses or hostnames are authorized to send email messages from your domain.

  • DomainKeys Identified Mail (DKIM): DKIM is a “digital signature” for each of your email messages that your subscriber’s ESP, like Google, Yahoo, or Microsoft Outlook, uses to identify and protect them from cybersecurity threats. Set up your DKIM to authenticate that your email is indeed coming from you.

  • Domain-based Message Authentication, Reporting & Conformance (DMARC): DMARC gives you finer control over your SPF and DKIM records. Check out our guide on implementing DMARC.

Why shouldn’t I send out bulk emails?

Use tools like our Email Automation API to send personalized, timely messages. Don’t use bulk emails, since most subscribers won’t engage with these impersonal messages. Remember, subscriber engagement affects whether or not your email ends up on the blocklist.

On a related note, you can also take advantage of our Send Time Optimization tool to contact your subscribers at the best time possible. This way, they’ll be more receptive to (and engage more with) your message when it lands in their inbox.

Why is it important to choose a service with monitoring features?

“In today’s digital landscape, where email deliverability is more and more important, landing on a blocklist can be detrimental to your ability to get messages in front of your subscribers. This impacts your bottom line, as well as your future sending. By proactively monitoring and addressing blocklist issues as they arise, you can safeguard your reputation, maintain customer trust, and ensure your messages aren’t automatically flagged as spam by ISPs.”

Kate Nowrouzi VP of Deliverability

What can I do if I get blocklisted?

If you find yourself on a blocklist, you can request to have your blocked IPs delisted:

  1. Consult what details you received when you were told you’d been blocklisted. Most blocklists will include a URL for you to begin the blocklist removal process. Follow their steps to get started.

  2. Send over the information requested by the blocklist vendor. Most reputable blocklists have a clear path to delisting. Usually, they require you to send them your contact information and any comments on the possible reason for the block. How were the open rates of those emails over the past few days? Have you received any spam complaints or hard email bounces recently? All of this information helps the support team sort out your case.

Not sure where to start? As a benefit of our Managed Service, we’ve automated monitoring of all major blocklists to check them in real-time. This means our team of experts will step in to deal with the blocklist providers on your behalf.

Wrapping up

Blocklists do serve a purpose. Without them, we’d have much more spam in our inboxes. And that, in our opinion, is way worse than a temporary listing.

There are many layers to email, and the reputation layer is important. Did you find these tips for avoiding the blocklist and some tricks for getting delisted helpful? Well, we’ve got lots more where that came from, but we practice what we preach so you have to opt-in to our newsletter to stay in the loop.

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