What are blacklists and how they work?

In email marketing, deliverability is key. To make sure your messages find their way into the inbox, you have to follow the best emailing practices. This includes good list hygiene, great content and compliance with email marketing laws. Failing to do so can get you blacklisted, jeopardizing your campaign success. That’s why we need to make sure you know the answers to the following questions: What are blacklists? how do blacklists work?

Why is blacklisting necessary?

Roughly 90% of the emails sent daily on a global scale are unsolicited. Without some kind of filtering, email users would be flooded with spam. Just imagine if all that spam got into your inbox. It would be impossible to find anything. Not to mention that all these emails take up server storage space, which doesn’t come cheap.

Blacklists are key components of most spam filters. ISPs use them to protect users from unwanted content and ensure that only good emails get through.

What are blacklists?

Email blacklists are real-time databases containing IPs and domains suspected of sending spam.

These blacklists identify spammers based on their IP address or domain. ISPs can check senders against selected lists to decide whether to allow emails to reach the inbox.

There are hundreds of blacklists out there: public and private, large and small. Some are available for a certain fee, but most of them are free to use.

Private blacklists cannot be accessed externally. There’s no way to tell if you’ve been listed until your emails start bouncing back. On the other hand, you can search public blacklists to see if your IP address or domain is listed.

Public blacklists are maintained by smaller independent networks, as well as large, reputable organizations. Not all of them affect your reputation and deliverability in the same way. It depends on their popularity and influence. Reputable blacklists used by major providers include Spamhaus, SURBL, Invaluement, Barracuda and Spamcop. Landing on any of the above will significantly affect your email marketing campaign.

In fact, most ISPs combine data from public blacklists and their internal lists to decide inbox worthiness.

how do blacklists work - learn this to improve email deliverability


Types of blacklists

Blacklists can be IP-based or domain-based.

IP-based blacklists

IP blacklists check the source of the email, i.e. the IP address to see if the sender is legit or problematic. Red flags include the use of open relays, open proxy servers and known spammers. Email service providers that allow spammers to use their infrastructure also get listed.

Domain-based blacklists

Domain blacklists are concerned with the sender domain. ISPs use them to check the URLs within the message body for domains identified as sources of spam. The check includes the initial link, but also where it redirects to.

Data collection methods for blacklists

Different blacklists use different approaches to build their databases. The same applies to their delisting requirements. Most of the time they collect the majority of their data through user input and spam traps.

User input

This method relies on user feedback. Senders are added to a blacklist if enough recipients mark their emails as spam. This method is used by free email service providers like Gmail and Hotmail.

Spam traps

Spam traps are “spam catching” addresses maintained by ISPs or third parties. They are not in active use and any traffic coming their way is by definition unwanted. Whenever a marketer emails to such addresses they get automatically labelled as spammers and put on that blacklists. Now, there are several types of spam traps you need to be aware of as an email marketer. So keep reading to find out.

Pure spam traps (honey pots)

These are addresses created as baits for spammers and placed on various websites. Spammers often use harvesting tools to gather addresses. These addresses are hidden from plain view, so only automated web-harvesters can find them. Repeated sending to honey pots can be detrimental for your sender reputation.

Recycled Spam Traps

Addresses that were once owned by people but have been closed or inactive for some time (each ISP has different lengths of time, some shorter and some longer). They are not as damaging as pure spam traps, but they do indicate poor list hygiene.

email spam traps can kill your deliverability

How do blacklists work?

Senders can get blacklisted if they fail to meet the criteria for legitimate sending of commercial emails. Blacklists don’t play an active role in email deliverability. They will affect your campaigns as much as the ISPs use them as guidelines for their filtering decisions.

Here’s how the process works. Blacklist operators monitor sending IPs and domains, and compile a list of offenders. ISPs can then consult these lists to help them sort good email from bad.

Understanding how blacklists work is crucial to your email deliverability. And your email deliverability is crucial to your profits as a marketer. Click To Tweet

Every time you send out a campaign, email servers check your IP or domain against one or more blacklists. If the IP or domain is listed, your emails are sorted as junk. If you are a multiple offender, the ISP will reject your emails automatically. In this case, they won’t even reach the junk folder.

Blacklists often share their databases of IP addresses and domains among themselves. That is why landing on one can be so damaging to your campaigns.

Blacklists and deliverability

Blacklists exist to aid in the battle against spam. But they can also affect legitimate senders like yourself. There is more to deploying email campaigns than just sending out emails. You have to consider all possible consequences. Otherwise, you can inadvertently cause deliverability issues.

Here’s a list of common blacklist triggers:

  • Sudden increase in sending volumes, which is frequently associated with spammers
  • Lots of spam complaints. Some amount of complaints is expected. People tend to forget they’ve opted in, so they mark you as spam. However, anything above the accepted level can be viewed as spammy behavior. As a result, your emails will get rerouted to junk or outright blocked.
  • Poor list hygiene, such as keeping inactive users on your list. Remember that inactive addresses can be recycled to serve as spam traps. Sending to harvested addresses (honey pots) is even worse. This practice can devastate your sender reputation.
  • Spam-triggering content in the subject line and message body.

Fortunately, blacklisting is usually temporary. Many blacklists delist senders after a while if no other spam attempts occur.

Are you on a blacklist?

There’s a simple way to tell if you’ve been blacklisted – just study your bounce logs. But the most convenient way to check this is by using Return Path’s Blacklist Alert. It will alert you immediately if your IP address lands on any of the more influential blacklists.

The Blacklist Alert also provides the reason for blacklisting. This way, you can resolve the underlying issues before your campaigns suffer additional damage. Make sure to monitor major blacklists and check your status frequently.

Monitor Your Status on Email Blacklists

You got blacklisted. Now what?

If you get blacklisted, your first reaction may be to request removal immediately. But keep in mind that getting off the list without assessing your emailing practices won’t do you any favors. If you don’t resolve the underlying issues, you’ll get back on that blacklist again. And in time, they will just start to automatically deny your future requests.

So, before you apply for delisting, learn why you got blacklisted in the first place. For instance, high complaint rates, sudden volume surges or poor list suppression process.

There are several ways to get delisted, depending on the blacklist in question. Most blacklists use the time-based removal approach. This means that they automatically remove the low level listings after a short while, like a week or two. It can take longer for serious offenders involved in multiple or high volume sends.

Some blacklists allow you to remove your IP manually (self-service removal feature). And if necessary, you can also communicate directly with the blacklist operator. For instance, if you aren’t sure why you ended up that blacklist. Or if you have already taken steps and resolved all the reasons for blacklisting.

Keep in mind that losing your temper or threatening to sue won’t get you far. Blacklist operators reserve the right to decide when to put you on a blacklist and when to remove you. It’s best to play it nice, cooperate and address all issues as soon as possible.

How to avoid getting blacklisted

When it comes to blacklisting, proactivity is by far your best approach. You can visit major blacklists and enter your IP to see your status. If you are on a list, take the necessary action without delay.

So, be sure to use good sending practices and don’t send out anything problematic. Keep a close eye on your sender reputation and do your best to maintain it.

Here’s what you should do to avoid getting blacklisted:

Steer clear from purchased lists

Mailing to rented or purchased lists is a high-risk acquisition practice. It may seem like a convenient shortcut to grow your list, but that’s all you’ll get. A long mailing list. And lots of spam complaints, instead of user engagement.

Send only to people that have opted in to receive content

The best way to collect addresses is to place a sign-up form on your high traffic sites. You can use the single or double opt-in method to add people to your list. With the single opt-in, you only ask them for their name or email address. In some cases you can even ask just for the email address alone and start sending them emails.

The double opt-in adds another verification layer. After they sign up, people have to reconfirm they want to receive mail. They can do this by clicking a confirmation link you email them. Double opt-in also prevents address misuse.

Be sure to add a clear permission reminder. This will remind people where and why they signed up to receive content from you.

Provide an easy way out

You should always try to give people what they want. This also means let them leave if they want to. Although this may seem counterproductive, people are more likely to stick around if you don’t pressure them to stay around. The more you make it clear that they can leave at any time, the more likely they are to stay around.

Make it easy for people to unsubscribe from your list if you want them to stick around. Counter-intuitive? Sure. Does it work? Most definetely. #email-marketing Click To Tweet

Always include a visible (and operational) unsubscribe link in all your emails. This is your legal obligation according to the CAN SPAM Act. Also, you have to process all unsub requests quickly (within 10 business days in the United States).

Adapt content to match user preferences

Segment your lists and create content tailored to people’s interests. Base your segmentation on opens and clicks, demographic data, past purchases or preferences.

Also, you can include a poll in your email campaigns and ask people what type of content they prefer and how often they want to get it. Use this data to tweak user segmentation and make more targeted campaigns.

poll your email subscribers for their preferences


Maintain proper list hygiene

Running your list through a list hygiene service is a good start. This will remove the majority of hard bounced emails, spam traps, and known complainers. There are many companies that provide list hygiene but don’t simply compare them by rates. Remember the old adage, “You get what you pay for”. They are not all created equal. We have worked with many list hygiene companies over the years and there are only a handful worth mentioning. A lot of our clients use and have had great experiences with Email Oversight. They are great to work with and very knowledgeable about list hygiene. They will work with you to get your lists to a good starting point by removing anything that shouldn’t be on your list. (reach out to bryan @ emailoversight.com and he will take care of all your needs)

Next get rid of the dead weight on your list, remove the users that fail to engage with your emails. It could be that the users abandoned these addresses or chose to filter your messages out. Either way, keeping them will only increase spam complaints and unsubscribes.

Before deleting them, though, run one last re-engagement campaign. Offer them an incentive like a free download or a promotion. If they fail to engage, delete them for good.

Register for Feedback Loops

Some mailbox providers offer a convenient service called a feedback loop. When you sign up for an FBL service, the provider will notify you each time a user marks your email as spam. You will receive a copy of the email (header and body) that generated the spam complaint. Also, you’ll probably need to set up an account specifically for this purpose.

FBLs help you eliminate poor leads from your mailing lists. They also provide useful insight into people’s response to your content and frequency. They can do a lot to protect your domain from getting bad reputation and earning the blacklist “seal”.

Be proactive

Keep close tabs on your complaint rates, unknown user rates and spam trap hits. Any increase in these rates calls for your immediate attention. Test your campaigns by sending different versions to a selected list and see what works best.

As a versatile email marketing platform, Emercury helps you do all this and more. You can use the split testing tool to test your campaigns. Simply change different aspects, like the subject line, sender name, delivery schedule or content.

The stats feature provides real-time insight into delivery, bounces, complaints and unsubscribes. The list hygiene tool helps you remove traps, bounces, complainers and bad addresses.

All in all, it’s not the end of the world if you get on a blacklist. Millions of marketers send millions of email campaigns every single day on a global scale. As a result, blacklisting is virtually inevitable for most marketers.

On your end, you have to make sure you stay at the top of your game. Work with an email marketing platform you can trust. Keep your lists clean, create awesome content and do regular blacklist checks.

Lastly, don’t forget that email marketing is not a one-time effort. Your campaigns are a continuous process that needs constant attention, evaluation and improvement.

Are you struggling with blacklisting issues? Emercury’s team of experts can help you put your campaigns back on the right track today

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