• The Warmup Inbox Team

Email Blacklists: What Are They (+ Removal Guide)

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




Being blocked by the mail servers is a common issue for many online marketers - not only for hackers or people with malicious intent.


In this guide, we will take a look at what exactly email blacklists are, how they work and how you can remove yourself from them.


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.


Blocklists 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.


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 a few 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 upon 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.


How many email blacklists are there?


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


Email blacklists are either IP Based: Real-time Blacklists (RBL) and Domain Name Server Black Lists (DNSBL); or Domain-Based: URI Real-time Black Lists (URL DNSBL).


There are four main types of email blacklists that can affect your emails:

  1. New Domain Email Blacklists

  2. Spam Trap Email Blacklists

  3. Phishing/Ransomware Blacklists

  4. Spam Blacklist

Out of the 300 email blacklists out there, there are eight that you really should stay off:

  1. Composite Blocking List by Spamhaus

  2. Spamhaus Block List (SBL)

  3. XBL Exploits Block List

  4. SpamCop

  5. Passive Spam Block List (PSBL)

  6. Invaluement

  7. Barracuda Reputation Block List (BRBL)

  8. Sender Score


Why does the email account end up on the blacklist?


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.


But you find out you’re on a blacklist anyway, don’t panic.


Depending on the type of blocklist, operators look for a few different factors when collecting IP addresses or domains.


The most common factors that will send someone to a blocklist include:


1. A hacked or spoofed email account


Most of the time, when a professional email ends up on a blocklist, it’s because a spammer hacks their account and sends out a large number of malicious emails under their IP address.


Sometimes, the company won’t notice that their account has been hacked until they run out of storage or one of their recipients just reports a weird email from “them.”


2. Using a “dirty” email list


If a company has a list of recipients for its newsletters or email campaigns, it must constantly update the list.


Consistently sending out emails to inactive or fake email addresses, falling into spam traps, or sending emails to people who unsubscribed from your content can land an IP address on a blocklist.


Additionally, if a company purchases a list of emails that claim to have “fantastic leads for the market,” then the list is likely composed of old emails or spam traps.


3. Emails reported as spam


If a sender’s emails end up in the spam or junk folders more than in the actual inboxes, the email provider may end up on a blocklist because of the number of complaints against the server.


One or two spam complaints won’t get you placed on a blocklist, but a plethora of spam complaints from your recipients or their ISPs will get you on a blocklist.

To maintain your reputation, you want to stay out of spam folders as much as possible.


4. Sending too many emails at once


If a sender doesn’t warm up its IP address and suddenly goes from sending a couple of emails per week to a couple hundreds a day, ISPs may think it is a spammer and place his IP address or domain on a blocklist.


This can be extremely frustrating, especially if you aren’t doing anything wrong - but as much as you may want to start sending out as many emails as possible, it’s essential to ramp up your efforts steadily.


How do I know if my account is blacklisted?


There are multiple online tools you can use to check if your IP address or domain is on a blocklist:

  • Barracuda Reputation Block List: free DNS blacklist that lists emails known to send spam

  • Invaluement: anti-spam DNSBL that blocks senders who send out unsolicited mass emails

  • MXToolBox: a way to check multiple blacklists quickly and check your DNS

  • MultiRBL: free multiple DNS service that cross-references lists by IPV4, IPV6, or domain

  • SpamCop: a list of IPs that have been reported as spam by SpamCop users

  • SpamHaus: DNSBLs used to identify and track spam sources

  • SURBL: lists of websites that have appeared in unsolicited messages

  • Warmup Inbox: as a part of our platform, we constantly run checks to make sure you’re not on any blacklists - every inbox synced to Warmup Inbox gets run by the 24 most common IPv4 blacklists to determine if your inbox and associated domain have been listed on one.

How to reduce the risk of being blacklisted?


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 - let’s take a look at each of them.


1) Verify your domain (SPF, DKIM, and DMARC)


Domain authentication signals that you are a legitimate user that sends the emails by himself (and not by some hacker).


The process of domain verification consists of 3 elements:

2) Avoid “spammy” content in 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.


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) 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.


5) 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.


6) 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.


7) Get and update your email lists naturally


Don’t buy email lists … ever.


There’s 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.


8) 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.


How to remove an account from an email blacklist?


Even if you took as many preventative measures as you could, you can still find yourself on an email blacklist.


The first thing to do is request to be removed from the list.

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.


Being removed from a Real-time Blackhole List (RBL) is often as simple as submitting a request to the blocklist administrator. Some of the popular RBLs you can request to be removed from include:

Some RBLs, like the Truncate Blacklist, will automatically remove users from their list after a period of good behavior from the domain or IP.


Unfortunately, some email accounts and domains cant 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.


Start landing in more inboxes. 
Use Warmup Inbox to improve your sender reputation and increase your deliverability.