Email Experts Series: The Ultimate Blacklist Primer

It’s the stuff of nightmares to any email marketer: blacklists. When you find yourself on one, you ask yourself a lot of questions, like how did this happen? What happens now? Can I get off it? What’s in the box?

Or perhaps you don’t ask any questions at all, because you’ve watched our newest Email Experts Series video, featuring Anthony Chiulli, director of product marketing, Beth Kittle, solutions architect, and Sloan Simmons, solutions architect.


(We’ve found key timestamps and transcribed this video below.)

Total Run Time: 14 minutes
00:35 – Defining an email marketing blacklist
01:30 – What are the differences amongst blacklists?
04:30 – How blacklists operate and what data they use in listings
05:22 – Ways marketers can identify and gain insight in knowing their are blacklisted
07:24 – What marketers should understand as a takeaway after being listed
08:48 – Common mailing strategies and seasonality that cause higher propensity for blacklistings
10:45 – Best practices and strategies for senders to take once blacklisted
13:20 – Information on additional resources and education on blacklistings

Listen and subscribe on your favorite platform:



Anthony Chiulli
Welcome, everyone. My name’s Anthony Chiulli, and today we are going to be talking about a very popular topic: an email blacklist. I’m joined today by my colleagues, Sloan Simmons and Beth Kittle. And my goal today with this conversation is really to just peel back maybe the negative perception of blacklists, and help our audience understand what they are, why they matter, how they’re powered, and also tips and tricks and recommendations on what to do once you’re listed. So let’s just start off very general, Beth, and just talk about, what is a blacklist?

Beth Kittle
Sure. So a blacklist is a real time list of IPs or domains that are suspected of sending spam. So ISPs, mailbox providers, and spam filtering companies will use these lists to inform their decisions on what gets through to the inbox. So from a consumer perspective, it’s kind of what keeps your inbox from being flooded with spam. But if you’re a marketer, you want to pay attention to these lists, because it could be what prevents your customers from receiving your mail.

Yeah. I mean, effectively, it’s a warning shot. Right? It’s a tool for mailbox providers and filter companies to slap your wrist or slap your hand as a sender if you’re doing something that’s not in accordance with their standards. Sloan, can you talk a little bit about the differences in blacklists? Because they’re not all created equally.

Sloan Simmons
Yeah. So there are hundreds. Hundreds of blacklists. There are many. At 250ok, we monitor over 40 IP blacklists and over 30 domain-based blacklists. So that’s two right there that you can focus on. And those are the main two that you’re really focused on. But there’s some that are out there specifically looking for a detection of malicious activity, and have different formulas for how they provide it. You focus on those two that I mentioned before. I could go out and grab 300 addresses and give it a silly name, and call it a blacklist, and it’s totally fine. That may not have the same kind of impact as a blacklist that’s been around, that’s respected, that people know in the community. Maybe even a blacklist that shows up at conventions and talks to people about why they do what they do, and some of how they do it. It’s often volunteers that come in and use different methods to identify who should be on a blacklist by their standards.

And I think it’s important to reiterate that, based on what you said, I completely agree and want to reinforce that a blacklist, they vary in impact, number one. But they are all designed to give you kind of a directional indication that something is wrong. What I often hear from brands in talking to marketers is, “Oh, no. I hit a blacklist.” And oftentimes there’s varying degrees of what that blacklist is. And it’s kind of this panic. Right? It’s like, “Oh, no. Everything’s going to shut down.” There’s all these misconceptions about what blacklists are, and their impact, and how they operate. But it’s important to know, too, that the reason that blacklists exist—their mission is to protect consumers from unwanted mail, malicious mail, spam. So it’s a notable mission. And that’s why they partner with so many different mailbox providers and filters, to help them protect their paying or non-paying users. The other thing that I wanted to talk about is many email box providers now, with the advancement of AI and machine learning and big data and sophistication, are able to kind of create their own suppression and blacklist. And I think that’s just an evolution in our space of the amount of data that mailbox providers have. They’re able to mine that data and see patterns and see signals to kind of really build proprietary blacklists as well. So it’s not only third parties and more notable blacklists like Spamhaus and a global provider like them, but also just very small mailbox providers, or well-known mailbox providers, that have their own proprietary. Beth, can you talk a little bit and explain how blacklist work, how they’re powered, and how they can basically list an IP or a domain?

Sure. So they’re looking a lot at spam trap addresses. So this could be old data that you’re sending to typo addresses. Pristine traps are email addresses that were never intended to receive mail from a real person. It’s just, they were invented with the specific goal of tracking spam. They’re also looking at complaints. So you mentioned mailbox providers have their own blacklists, and they’re looking at people who are essentially marking mail as unwanted. If there’s a large enough spike in those kinds of metrics, you may end up on a blacklist.

Sloan, what about visibility and actually knowing that you are blacklisted? I feel like many senders probably are listening to this and thinking, “I wonder if my IPs and domains are on blacklists?”

Yeah. So this is a really good point off of what Beth just mentioned, where when you’re looking at the effects from a mailbox provider, and you see maybe it’s a bunch of trap addresses or trap addresses that were harvested, that were created for the purpose of being trap addresses. And then all of the sudden, you get a bunch of bounce messages that come in, saying no mailbox exists. Or maybe it always accepts mail and never responds to anything, and you’ve had it in your list for two years. It’s never opened once. But it always accepts. These are common ways that you can start looking through your engagement activity, both bounces and general engagement, like clicks and opens, to be able to start identifying, “Oh, okay. Maybe I need to look at some of my engagement metrics for a lack of activity and opens.” But you also have bounce messaging that you can start identifying: “Okay. I’m getting a huge spike in trap addresses. I’m also getting a huge spike in bounce messages. Let me go look at the bounces. Let me look at the bounce messaging to see if there’s something in there that says a whole bunch of dead address. There’s nobody here.” So there’s a lot of ways you can use your ESP or a tool like us to identify, one, the volume of traps you’re getting across something like a censor network, but also use it against your segmentation. If you have a list source that is coming in, and you create a segment based on it, monitor it. See if you hit more traps. See if you end up getting worse open rates and higher bounce rates from your sending platform, to see if you can measure the impact that you’re getting from a blacklist.

What should a sender do– Or let me rephrase that. What should a sender take away from hitting a blacklist? What is the self-reflection that, in your opinion, a sender should understand about hitting a blacklist?

Definitely. So there’s one thing I want to unpack, which is a really common misconception, and it’s a blacklist versus a block list. So we talked about mailbox providers and how they can have their own blacklists. But you have something that is a direct impact from hitting a bunch of trap addresses built by these networks. And the impact you’ll see is maybe— Microsoft is a really good example, because they give a bounce message that specifically says, “Your IP is blocked due to X reason. Go to this form to start your remediation process.” And there’s a few out there that are more major players that’ll say that. Or they’ll say in the message itself the keyword, which is the blacklist. So you can do a search in your bounce messages for the name of the blacklist you find yourself on, and monitor the impact. So this is usually indicative of some kind of list health issue. It’s almost always a list health issue. How did you collect it? Are these addresses old? What’s the engagement value? And what’s the value you’re getting from holding onto addresses, or the way that you collected these addresses?

Beth, I’d love to get your opinion on frequency or seasonality of blacklists, and when senders—whether it’s specific use cases or time of year that blacklists are more frequent.

Sure. I mean, I think anytime senders are sort of interested in ramping up their volume—maybe it’s a Black Friday, or based on the industry, their own peak seasons may vary. But there’s definitely times where senders are going to be increasing their volume or expanding their targeting. Maybe you have a new list source, or we often see spikes, too, around re-engagement campaigns, because senders are reaching out to people who haven’t been active with their email in a long time. And those could be trap addresses at this point. They could be users that just will end up complaining because they haven’t seen your mail in their inbox for so long. So that’s kind of when we see an uptick for senders.

Yeah. I would agree. I think anytime, to your point about the sources of blacklists, it’s usually driven by either/or a combination of spam traps and complaints. And so anytime a sender is digging deeper into their file, or perhaps some sort of questionable new list source that they’re wanting to take on to drive more revenue. And oftentimes that does align with peak season or Black Friday, Cyber Monday, where they’re just trying to get as much bang for their buck as they can. But ultimately what ends up happening is, the irony is you end up inflicting and hurting yourself more by trying to generate more revenue. So it comes with a measurable amount of risk any time a marketer starts to go beyond their comfort zone and their targeting, their acquisition sources, and things like that. Follow-up question for you, Beth, is, now that a sender—let’s say a sender is listed. They find themselves on a blacklist. They’re made aware with the visibility in tools and alerts. What now? What are the common best practices for a marketer or sender once they become blacklisted?

Sure. I think to Sloan’s point, often I recommend, look at your bounce reasons and see, is the blacklist being called out? Do you see a high impact from that bounce list? Excuse me, from that blacklist. And if you do, there are usually remediation forms for your—you can enter your IP or your domain, where you’re actually reaching out to the blacklists. And they can give you some information sometimes on traffic that they’re seeing that may have been problematic. And then again, it is typically a list hygiene issue. So going back and sending to your most engaged recipients. And you always want to—something we recommend to senders a lot is having a really strong sunsetting policy. So maybe for your business, it makes sense to remove inactive addresses that haven’t engaged with your lists in the last six months, or whatever the time frame is that makes sense for you. And then just constant monitoring. Monitoring your spam trap hits. We have tools for that. And our product that can kind of make you aware of when there are upticks in spam trap traffic, then kind of drill down to what days did you see those spikes on. And that can sort of help point you to a list or a data source that might be problematic for your mail stream.

So I think it’s really important that you mentioned the re-engagement campaigns, because it is both sides of that coin where it is really often that a re-engagement campaign could be the reason you’re on a blacklist. But it’s also required because you don’t necessarily just want to cut everyone from your list. You want to be able to find people that are still interested, but also mitigate the damage. So you do this through the segmentation process and re-engagement welcoming or re-welcoming campaigns, sunsetting strategies. They’re all natural to the email process. It’s just a matter of making sure that you can take care of the damage as it comes along the way as well.

Well said. Well said. I wanted to encourage all of our audience to take a look at our blogs on the 250ok website. We’ve blogged extensively about blacklists and 101s to guides about educating about blacklists. I think this has been extremely informative and helpful. And blacklists is this topic that most marketers have hit at least one in their time. Especially if they’ve been around. But they’re easily avoidable if you understand how to mitigate the risk, when they’re usually more prominent to pop up, how they’re powered. Right? The most common reasons that you’re hitting blacklists. And as you talked about, Beth and Sloan, ways to remediate once you have hit a blacklist. So thank you guys both. This has been a great conversation. And thanks everyone for tuning in.

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