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Email Blacklists: Everything You Need to Know in 2024

Updated: Apr 12

If you are having trouble sending emails to your recipients, you might have ended up in one of the blacklists.

Sounds scary, but it’s a common problem that many email marketers face.

In this article, we will cover everything you need to know about email blacklists. Starting with:

Email Blacklist Removal

What is an email blacklist?

An email blacklist is an online collection of IPs or email addresses with severely damaged sender reputations.

Mail servers use these lists as a reference to determine how safe it is to accept emails coming from unknown domains and addresses and therefore protect consumers from receiving malicious or unwanted messages.

Blacklists can cause many problems for your marketing campaigns - if your email address ends up on a blacklist for any reason, your emails won’t get to your subscribers.

Here are a few of the most well-known blacklists:

  • Spamhaus Block List (SBL): Targets known spam sources.

  • Barracuda Reputation Block List: Focuses on IP addresses with poor reputation scores.

  • SpamCop: Users report spam, leading to IP address blacklisting.

  • Sender Score: Rates the reputation of email senders.

  • URIBL: Blacklists URLs found in spam emails.

How do email blacklists work?

A blacklist acts as a reference point for other mail servers to determine the history of another domain online.

A general rule of thumb regarding how blacklists work is that if you participate in email activity that can be interpreted as spam, malicious, or unwarranted then it can end up landing you on a blacklist.

When you send an email, the recipient’s server checks your IP address against multiple DNS blacklists - if your address doesn’t match any of them, the ISP will run several other security checks to see which folder to put your message in.

However, if there is a match on one of the lists, the ISP will not let your message through.

Blacklists exist for the benefit of the Internet in general, as they act as a “No Entry” list based on what negative behavior other mail servers have reported.

While these lists aren’t the only thing that affects deliverability, they can have a severe and sudden impact if you end up on one.

A simple example of how a blacklist works is when an email service provider uses a list, like the Spamhaus Block List, to check incoming emails.

If the email's source IP address is on the list, the email is flagged as spam and blocked, or routed to the spam folder, preventing it from reaching the recipient's inbox.

While this process helps protect users from receiving unwanted or harmful emails, reputable senders may accidentally end up getting on these lists.

Types of email blacklists

Given how diverse the email world can be, there are, in turn, several types of blacklists in use today.

  • IP blacklists: These target specific IP addresses that have been flagged for sending spam. An email address can end up here if it sends too many unsolicited emails.

  • Domain blacklists: Focus on the domain part of an email address. If a domain is known for sending spam, all emails sent from it might be blocked.

  • Public blacklists: Accessible by anyone, these lists are often used by email service providers to filter out spam. You can end up here from being reported as spam, a high number of user complaints, or falling into a spam trap.

  • Private blacklists: Maintained by individual organizations for internal use and not publicly accessible. Ending up on a private blacklist usually occurs through direct interactions or transactions with an organization that maintains its own list.

  • Spam firewalls: These are dynamic systems that block emails in real-time based on spammy content or behavior.

The most popular email blacklists

There are over 300 known email blacklists that anyone can access - some of them have a bigger impact than others on your email deliverability.

Here’s a list of some of the most common blacklists, what category they fall under, and what makes them tick - each blacklist has its own methodology for identifying potential spam sources, contributing significantly to filtering efforts across the Internet to maintain email hygiene and security:

  • UCEPROTECTL1 (IP based): Targets individual IP addresses showing spam behavior. By monitoring spam traps, IPs get listed when they send spam to these traps.

  • UCEPROTECTL2 (IP based): Escalates to list entire ISPs if a large enough portion of their IP range is found on UCEPROTECTL1, indicating a broader issue with spam from that provider.

  • UCEPROTECTL3 (Spam based): UCEPROTECTL3 lists entire countries or large networks if spam is pervasive across many ISPs within a region, based on listings in UCEPROTECTL2.

  • SORBS (Public/IP based): Operates by listing servers and IP addresses that have been reported as sources of spam, open relays, or have vulnerabilities that spammers exploit.

  • Suomispam (IP based): Focuses on identifying and blacklisting IP addresses involved in sending spam to Finnish email users or originating from Finland, utilizing user reports and trap accounts.

  • Spamhaus Block List - SBL (Public/IP based): A highly respected blacklist that includes IPs identified as sources of spam or involved in spam operations, using investigations and reports.

  • Truncate (Spam based): Automatically lists the most aggressive spam sources based on real-time analysis of spam reports and patterns.

  • Barracuda (Public/IP based): Maintains a reputation system for IP addresses based on reports of spam and other malicious email activities from its network of users.

  • SpamCop (Public/IP based): Allows users to report spam, which SpamCop uses to identify and list offending IP addresses. It's dynamic, with listings based on recent reports.

  • SpamRATS (Public/IP based): Lists IP addresses associated with spamming, especially those from compromised servers or known to send out spam without authorization.

  • Passive Spam Block List - PBSL (IP based): Focuses on IP addresses sending low-engagement emails, using spam traps and feedback to identify offenders.

  • Exploits Block List - (IP based): Identifies IPs compromised by malware or viruses that are known to send out spam or malicious content.

  • ZEN Spamhaus (IP based): Combines several Spamhaus lists for a comprehensive overview of IP addresses involved in spamming or hosting malicious sites.

  • WPBL (Private): A community-driven list that collects reports on websites and IPs associated with spam activities.

  • MultiRBL (Multi-DNS based): Aggregates data from multiple blacklists, offering a broad spectrum analysis to identify spam sources.

  • SURBL (spam based): Focuses on URLs within emails linked to phishing, malware, or spam content, helping to block harmful messages.

  • Invaluement (spam based): Specializes in catching elusive spam that often bypasses conventional filters, using a sophisticated analysis mechanism.

  • SenderScore (IP based): Provides a reputation score for email senders based on their sending behavior, including spam complaints and sending volume.

  • Senderbase: Operates similarly to SenderScore, evaluating domains and IP addresses to rate their email-sending practices.

Why do email addresses get blacklisted?

Blacklists were created to protect the general public from unwanted emails, and if you aren’t a spammer, you shouldn’t have any issue getting yourself off a blocklist.

There are plenty of ways to get blacklists, but thankfully, most are easily avoidable by following emailing best practices. Nevertheless, it just takes a few simple errors to end up blocked.

Here are the main reasons you might find yourself blacklisted:

  • Poor email hygiene

  • High email bounce rates

  • A lot of spam reports

  • Sending emails to spam traps

  • Creating poor or spammy content

  • Hacked or compromised email account

Now, let’s dig in a little further.

a) Poor email hygiene

Neglecting to clean your email list can lead to a higher rate of sending messages to non-existent addresses.

This not only wastes time and money but also signals to email providers that your list management practices are subpar, affecting your sender's reputation.

Imagine you’re running an online pet supplies shop and sending out weekly newsletters.

Over time, without regularly cleaning your email list, it includes many addresses that are no longer active, or incorrectly entered.

As your emails consistently bounce or get marked as spam by recipients who no longer want to receive them, these indicators flag your activity as potential spam.

Eventually, an email blacklist operator will notice the pattern and add your shop’s domain to their list.

b) High Email Bounce Rates

Email addresses that consistently return a high volume of bounced emails tell ISPs that the sender might not be verifying their email list.

This lack of verification can quickly lead to being marked as a spammer.

Consider a small business launching an email campaign without a clean, verified email list.

Because of outdated or incorrect addresses, a significant portion of emails bounce back.

This high bounce rate signals to Internet Service Providers (ISPs) that the business may not be maintaining its email list, which could quickly categorize the business's email domain as spammy, leading to potential blacklisting and hindering future email deliverability.

c) A lot of spam reports

When recipients frequently mark your emails as spam, it directly impacts your sender score.

Too many spam complaints can trigger automatic systems to classify your emails as unwanted, leading to blacklisting.

Let’s pretend a newsletter for a new health and wellness blog is eagerly sent to a broad audience.

Despite the good intentions, many recipients, uninterested or having signed up unknowingly, flag the emails as spam.

This reaction adversely affects the blog's sender score, triggering ISPs' algorithms to categorize further emails from the blog as spam, risking a blacklist placement and jeopardizing the blog's email outreach efforts.

d) Sending emails to spam traps

Engaging in practices that inadvertently send emails to spam trap addresses indicates to email service providers that your list might be harvested unethically or poorly managed.

Picture a marketing team, in their zeal to reach a wide audience, buying an email list and starting to send out promotional content.

Unbeknownst to them, this list includes several spam trap addresses.

Email service providers, detecting emails sent to these traps, may conclude the list was not responsibly sourced, reflecting poorly on the team’s email practices.

This situation could lead to their domain being flagged, affecting email deliverability and reputation.

e) Too many outbound emails

Sudden spikes in email activity can appear suspicious, as it resembles behaviors typical of spammers.

Maintaining a consistent and reasonable email-sending pattern is crucial.

f) Creating Poor or Spammy Content

Content that is overly promotional, lacks relevance or is filled with spammy keywords can trigger email filters.

Effective content should be engaging, relevant, and provide value to the reader.

g) Hacked or Compromised Email Account

An account that has been taken over by a malicious actor can start sending out large volumes of spam.

Such activities tarnish the reputation of the email address and can lead to immediate blacklisting.

How to find out if your email is blacklisted

Understanding whether your email has landed on a blacklist means you have to keep an eye on certain indicators – such as unusually low deliverability rates, spikes in bounce rates, or explicit notifications from email services indicating that your email has been blacklisted.

Low deliverability rate

A low deliverability rate might mean your emails are being blocked or sent to spam folders, which can happen if your email address or domain is blacklisted.

Analyze your email campaign reports for consistent drops in deliverability. Tools within your email service provider can offer insights.

Spike in bounce rates

A high bounce rate, especially with hard bounces (emails returned due to invalid addresses), may signal that your sending practices are problematic, potentially leading to blacklisting.

Monitor your email bounce reports closely.

A sudden increase in bounces might require further investigation using online blacklist-checking tools.

Email service notifications

Receiving a direct notification or seeing warnings in your email platform's reports suggests you've been added to a blacklist.

Upon receiving a notification, visit blacklist monitoring websites such as MXToolBox or MultiRBL.

Enter your domain or IP address to search across various blacklist databases.

To investigate further, you can try out some of the following methods.

Send a test email

There are plenty of platforms where you can send test emails to see how they perform, and whether they land in the inbox or spam folder.

These services are great for helping you understand your email deliverability rates and make necessary adjustments to improve open rates.

Tip: Interested in a totally free service that can quickly check what inbox your email will end up in? Check out our free inbox placement tool!

Use an email monitoring tool

Because blacklists are such a common frustration for email marketers of all types, there are plenty of tools that can do the heavy lifting for you by continuously scanning all the major blacklists to see if your email is listed.

Warmup Inbox also includes a blacklist monitoring tool that continually checks if your email address or domain has been blacklisted.

By staying informed about your blacklist status, you can take immediate action to resolve any issues, ensuring your emails reach their intended recipients.

Try email blacklist checkers

EmailListVerify offers a free tool to check if your email is on a blacklist. Additionally, services like MXToolBox and Barracuda provide comprehensive checks across multiple blacklists, helping you understand your email's status better.

Here are some other popular options to keep in mind:

  • Invaluement

  • MultiRBL

  • SpamCop

  • SpamHaus


How to avoid email blacklists?

Getting placed on a blocklist can feel like a worst-case scenario, but as frustrating as it is, it’s something that can be fixed or prevented with a small investment of time and effort.

There are a few defensive measures that you can take in order to avoid having to go through the hassle of being blacklisted.

Follow these best practices to keep yourself in good standing with the email gods:

  1. Authenticate your domain

  2. Avoid spam words your emails

  3. Use a dedicated IP

  4. Secure your server

  5. Send emails only to your subscribers

  6. Don’t send too many emails right away

  7. Warm up your inbox

  8. Use a double opt-in method

  9. Provide an unsubscribe link

  10. Don’t buy email lists

  11. Verify the email addresses of your subscribers

  12. Maintain a positive sender reputation

  13. Personalize your emails

  14. Don’t add email addresses to database manually

  15. Provide whitelisting instructions

  16. Remove invalid or inactive subscribers

  17. Monitor your email metrics

1. Authenticate your domain

Implementing SPF, DKIM, and DMARC records for your domain is extremely important for staying off blacklists.

The process of domain verification consists of 3 elements:

These authentication techniques verify your identity as the sender, building trust with email service providers and helping your emails reach the inbox.

2. Avoid spam words your emails

Spam filters and mail servers can be very picky about the content in your emails.

If your email contains certain keywords, spammy phrases, or even links to suspicious websites, your message can end up either in a spam folder or being outright blacklisted.

Tip: Our free spam words checker can help you refine your email content, which helps make sure your messages aren't mistakenly flagged as spam due to unfortunate wording.

3. Use a dedicated IP

Dedicated IPs are exclusive channels for internet use and offer significantly more control over IP reputation.

Dedicated IPs cost more but are an excellent investment for companies that rely on email marketing to connect with their customers.

With a dedicated IP, you’re decreasing the chance that somebody would use your address for malicious purposes - and the unfortunate result of being blacklisted at the end.

4. Secure your server

Making sure your email server is secure against unauthorized use is vital. A compromised server can be used to send spam, leading to blacklisting.

5. Send emails only to your subscribers

Sending messages to those who have explicitly subscribed to your list is fundamental.

Unsolicited emails are a direct path to blacklists; thus, respecting user consent is key.

6. Don’t send too many emails right away

Sending emails in bulks can severely damage your email reputation in a very short period of time.

Starting with a small number of emails and gradually increasing the volume can help warm up your email address and slowly establish a positive reputation with ISPs.

7. Warm up your inbox

Sending out too many emails out of the blue is a common mistake for many email marketers - even though your intentions might be good, it is a sure way to get blacklisted.

By warming up your email account first, you can slowly but surely get trust from email and ISP providers and avoid any common email blacklists out there.

Warmup inbox allows ISPs to recognize you as a trustworthy sender and will get your future messages sent right to your recipient’s inbox.

Aside from staying off of blocklists, warming up your email and domain help you:

  • Maintain and improve your email deliverability

  • Increase your sender reputation with ISPs

  • Increase the total number of emails your domain can safely send

  • Help prevent your domain from being considered spam

  • Keep your outgoing emails out of spam traps

Warming up an email address takes a fair amount of time, but it’s worth the effort.

Email marketing is one of the most beneficial modern marketing tools, but it can’t work for you if you can’t get into your customer’s inboxes.

When done right, email campaigns can have an ROI of up to 4400% or $44 for every $1 spent, so why take the chance of missing out on the capability your company has for growth?

You can try Warmup Inbox for free to see how you can seamlessly and effortlessly warm up your IP.

8. Use a double opt-in method for new subscribers

Have your customers verify that they want to receive your emails and give them the chance to confirm that their email is correct before you start sending them messages.

By implementing the double opt-in method, users can have an opportunity to let you know in advance that they want (or don’t want) to receive your emails - which will help you to avoid “spamming” those who are not interested in your email campaigns.

9. Provide an unsubscribe link

If you give customers the chance to unsubscribe from your emails, they can request to stop receiving emails from you instead of flagging your content as spam.

Just be sure to honor their request (and CAN-SPAM compliant) as soon as you can - otherwise you can receive too many spam reports and end up being blacklisted quite quickly.

10. Don’t buy email lists

There’s always a chance you may encounter someone selling email addresses that fit your target demographic.

This may seem like an easy way out, but these lists are often filled with fake emails and/or spam traps - which are a sure way you can end up on the email blacklists.

Although it may take longer to gather emails organically, it’s much better for you in the long run.

The same principle applies to email list updates - if an email bounces, remove it from your list or find a way to correct the email address if it’s typed in wrong.

Multiple bounced emails indicate that you’re randomly sending out emails and can damage your reputation.

11. Verify the email addresses of your subscribers

Before sending out email blasts, verifying emails can prevent bounces and maintain a healthy sender reputation.

12. Maintain a positive sender reputation

ESP providers will maintain a separate sender score for each individual inbox under a domain.

This is the most important factor for determining the overall deliverability of any given inbox under a domain.

Whenever an email service provider is determining the placement of incoming messages, they will refer to the history of the IP address associated with the domain of the email as nearly all sending history is tied to this value.

Anytime an email bounce gets delivered, or gets sent to a spam folder,email service providers take note and calculate a reputation score to assign to this IP address.

This reputation score is then shared among other email and internet service providers in order to provide a reliable idea of how trustworthy a sender/IP address is before accepting any mail from it.

13. Personalize your emails

Making your emails more personal can drastically reduce the chances of being marked as spam.

Addressing recipients by name and specifying content to their interests, you both improve reader engagement and steer clear of blanket approaches often associated with spam.

14. Don’t add email addresses to your database manually

Adding emails without explicit consent can lead to spam complaints. Always seek permission before adding anyone to your list.

15. Provide whitelisting instructions

Encouraging users to add your email address to their contact list improves deliverability and ensures your emails consistently reach the inbox.

16. Remove invalid or inactive subscribers

Regular list maintenance to remove unengaged subscribers can improve your engagement rates and reduce the risk of spam flagging.

Use tools like EmailListVerify to purge invalid or non-responsive email addresses, guaranteeing high deliverability and engagement.

17. Monitor your email metrics

Keeping an eye on important email metrics like open rates, bounce rates, spam complaints, and your sender/domain reputation helps you adjust your strategies for better inbox placement.

How to get off email blacklists?

Unfortunately, even if you’ve taken as many preventative measures as possible, you can still find yourself on an email blacklist.

This doesn’t mean you’re a bad emailer by any means – these systems are imperfect and can make mistakes.

The first thing to do is to request being removed from the email blacklist.

Sometimes this is as easy as submitting a request to the blacklist provider; other times, you’ll have to prove to the provider that you’re a legitimate company and you’re working toward creating a better reputation for your email address.

Blocklist operators may ask you to complete a couple of tasks or implement a new protocol before removing you from the list.

For instance, they could require that you send your subscribers a re-permission request that allows them to express that they want to continue receiving mail from you.

Other times the blocklist operator may ask that you put a double opt-in subscription policy if you don’t have any.

Keep in mind that being removed from a list is often on a case-by-case basis, and you may not always have control over being removed.

a) Run a permission pass campaign

A permission pass campaign involves reaching out to your email list to confirm their interest in continuing to receive your emails.

This step is vital for ensuring that your email list is engaged and compliant with anti-spam laws.

It's a proactive measure to clean your list and help email deliverability.

  1. Segment your email list to target inactive or uncertain subscribers.

  2. Design a clear, concise email asking for their explicit permission to continue receiving your emails.

  3. Include a straightforward opt-in link or button in the email.

  4. Send the permission pass email to the segmented list.

  5. Track responses and remove anyone who doesn't opt in or actively chooses to unsubscribe.

  6. Update your email list to reflect only those who have confirmed their subscription.

b) Send a blacklist removal request

To send a blacklist removal request, first identify which blacklist you're on.

Then, visit the blacklist's official website to find their specific removal procedures.

This typically requires filling out a delisting request form, where you'll explain the corrective actions you've taken to address the issues that led to your blacklisting.

Follow up as necessary, but remember, removal isn't always instant and may require additional steps based on the blacklist's policies.

c) Wait for the time-based removal

Some blacklists automatically remove entries after a specific period if no further negative activity is detected from the email sender.

This time-based removal process can vary by blacklist, with some requiring days, weeks, or even months before delisting occurs.

During this waiting period, be sure to address any issues that led to the blacklisting and avoid additional infractions.

d) Try self-service removal (if possible)

For self-service removal from an email blacklist, many blacklists provide a process on their website where you can request to be delisted.

This typically involves verifying ownership of the email address or domain and confirming that the issues causing the listing have been resolved.

Note: After being removed from a blacklist, it's essential to continue best email practices to avoid future listings, such as maintaining list hygiene and monitoring for spam traps.

e) Start from scratch

Unfortunately, some email accounts and domains can't be redeemed - if there is no way to remove your address from the list, you may need to start over with a new IP address.

When setting up a new IP address, make sure that you take protective measures that will prevent you from ending up on the blacklists again.

Frequently asked questions

What is an email blacklist?

How do emails get blacklisted?

What happens if I get my email address blacklisted?

How to check if my email address is blacklisted?

How to avoid email blacklists?

How to remove myself from an email blacklist?


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