Email Blacklists

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Have you ever received a speeding or traffic ticket? How about two? Three?

Once you get enough tickets on your record, your license will be suspended until you can prove that you’re a safe driver. Blacklists work the same way.

What is a Blacklist?

Email blacklists are a real-time list of servers and domains that are known to send spam. This is similar to a driver with a poor driving record.

There are two type of blacklists:

  • IP address blacklist:  A specific IP or multiple IP addresses that are suspected of sending spam or abusive emails.
  • Domain blacklists: A domain that is found to be sending spam and deceiving its users.

Nearly 85% of all emails sent daily are considered spam. Blacklists were created to protect email recipients from spammers.

How do blacklists work?

Every time you send an email, the recipient’s mail server will decide where your email should go. One key part of this process is when the recipient’s spam filters check to see if the sending IP or domain are blacklisted.

Each spam filter will include their own set of blacklist rules and policies- some stricter than others.

Major Blacklists:

There are hundreds of blacklists. Major blacklists will tank your deliverability by causing emails to be rejected or sent straight to spam.

Spamhaus, the operators of one of the largest blacklists, created the graphic below that showcases how and when a blacklist interacts with an email.

How can I end up on a blacklist?

There are several factors that can cause your domain or server IP to be blacklisted.

High Spam Complaint Rate: Every time a recipient marks your email as spam it will increase the probability of becoming blacklisted.
Emailing spam traps: These are emails that are no longer in use and are recycled by mail servers to catch users with poor list hygiene.
Compromised Server or Application: If your server becomes compromised spammers can send thousands of emails on your behalf.

How can I avoid being blacklisted?

  1. Send relevant emails: Send emails that are relevant and engaging. This will reduce your spam complaints and keep your list engaged.
  2. Use the List-Unsubscribe Header: Allowing your subscribers to unsubscribe easily will reduce spam complaints. We suggest using an email service provider that automatically supports these headers.
  3. Don’t email inactive subscribers: Remove subscribers who haven’t opened or clicked any of your emails in the last 3 months. This will improve your domain reputation, and reduce the likelihood of hitting spam traps in the future.
  4. Don’t email spam traps: Clean your email list periodically with NeverBounce . This will prevent you from emailing any spam traps, unused emails, emails with typos, or fake emails.
  5. Authenticate your Domain: Setup SPF, DKIM and DMARC on your domain. This will prevent spammers from ruining your domain reputation.
  6. Setup double opt-in: Send a confirmation email before adding a new subscriber to your email list. This will improve open rates and click-through rates while reducing spam reports and unsubscribes.
  7. Provide Whitelisting Instructions: Provide your users with instructions on how to whitelist your domain so each email you send goes straight to their inbox. This will improve your domain reputation by showing that you’re a legitimate sender.
  8. Avoid purchased lists: Purchasing an email list is dangerous because some of the email addresses may be invalid or spam traps. This can lead to blacklisting, bounces and an increase in spam complaints by sending to a non-opt in list.
  9. Use Real-Time Address Validation: Check email addresses during the signup process for validity and common typos. This will reduce fake emails, common domain typos and pristine spam traps.

How can I check if I’m blacklisted?

There are a lot of blacklists, but a good starting point is checking to see if your IPs or domains are on any popular blacklists.

You can run a free test at to see if you’re listed on any major blacklists.

What do I do if I’m blacklisted?

If you’re listed on a major blacklist this will have a direct impact on your deliverability by causing your emails to be rejected or sent straight to spam.

In order to get removed from a major blacklist you need to understand their delisting process. You also need to find out why you were listed and how to prevent it from occurring again.

Tip: You can message the MailGenius team on live chat if you need help getting delisted from a blacklist.

Types of Blacklist Removal:
  • Self-Service Removal. There are a few blacklists with a self-service removal feature that let you take your IP address off their list without much trouble. However, it’s important that your IP address doesn’t get listed again because it will be more difficult as a second offense.
  • Time-Based Removal. Most blacklists have a built-in, automatic process that removes lower-level listings (IP addresses that are light offenders) within a week or two. But if the IP address had sent spam more than once or did a high volume, the time period will be longer.

When you’re trying to get off a blacklist, you’ll get farther along if you follow the rules and cooperate. If you are truly innocent of any deliberate wrongdoing (or if you made an honest mistake), let the blacklist provider know.

The more open and direct you are with a listing database, the simpler it may be too have your IP address taken off the blacklist.

Remember a Blacklist’s provider priority is to reduce the spam on their email platform for their customers—their goal isn’t to prevent you from sending emails.

Spam is a serious problem. They don’t blacklist lightly. It’s their way of trying to identify and prevent real problems.

What does the MailGenius email test tool cover with regards to blacklists?

Each time your run a MailGenius test we check to see if your sending IP,  domain or links within your email are listed on any of the major blacklists below:

  • PBSLPassive Spam Block List: You get listed by sending emails to their spam trap addresses.
  • CBLComposite Block List: Your IP gets listed with malicious behavior such as spam bots, dictionary attacks, open proxies and similar attacks. This may occur after a web application has been compromised.
  • SBLSpamhaus Block List: You get listed by sending emails to SBL spam trap addresses. This may happen after your server or website has been hacked and emails have been sent from your system.
  • XBLExploits Block List: You get listed when your PC has been hijacked and infected by illegal 3rd party exploits, such as open proxies, viruses with built-in spam engines, and other trojan-horse exploits.
  • BRBL Barracuda Reputation Block List: You get listed by sending spam directly to Barracuda Reputation System’s detectors.  These can be honeypots, spam traps and other spam sources. This may occur due to a security issue on your server.
  • SpamcopSpamcop Blocking List: Spamcop uses a reputation score based on spam traps and spam reports. You get listed when your score drops too low. This typically occurs due to a security issue on your server.
  • ZEN ZEN Spamhaus: ZEN is a combination of all Spamhaus IP-based DNSBLs which include the SBL, SBLCSS, XBL and PBL blocklists. This comprehensive blocklist makes querying faster and simpler.

Caveats, things to watch out for:

Recycled Spam Traps: These are email addresses that were valid, but are now dormant. Sending an email to a spam trap can set off spam filters due to poor list hygiene.
Typo Traps: These are email addresses that end up on recipient lists due to user error. Typing [email protected] instead of [email protected] Sending excessive amounts of email to typo traps shows poor list acquisition practices.
Pristine Traps: These are email addresses and domains that have never been used to actively sign up to receive emails. Pristine traps most commonly end up on mailing lists when senders purchase, rent, or scrape addresses.

MailGenius Tips and Tricks

We suggest using Hetrix Tools to proactively monitor your IP’s and domain to ensure they don’t become blacklisted.

With Hetrix tools you can:

  • Clean up your network and domains, and then keep them spam-free
  • Improve your network’s reputation and email deliverability rate
  • Find out which of your servers or websites may be infected with malware
  • Locate spam/malware sources within your network as soon as they appear
  • Manage your IP space, so you can always assign clean IPs to your new clients

Use code Mailgenius to save 50% off your first month’s invoice (if billed monthly), or 10% off the first year’s invoice (if billed yearly).

Additional Resources

  1. Email Blacklist: How to Tell If You’re on It (and What to Do If You Are)- LeadFuze
  2. What Are Email Blacklists and How to Avoid Them- SendGrid
  3. How should I check if my email has been blacklisted?- LeadFuze
  4. Understand email blacklists- HubSpot
  5. Email Blacklists 101: What You Need to Know- Campaign Monitor
  6. How to Remove an IP Address from a Blacklist- WhatIsMyIPAddress
  7. The 8 critical Email Blacklists – rackAID
  8. Get Your Questions Answered by Real Email Experts –