Introduction

Getting into email blacklist is the most common cause of email delivery issues. Once the domain or IP address is in the blacklist, you will automatically see a surge in spam complaints and hard bounces. All these will impact your brand reputation and finally a dip in the email open rates too. Using an Email Blacklist Checker is critical for anyone who is using email marketing as their primary marketing strategy for revenue and lead generation. 

Email blacklist can be done on two factors one is the IP address of the mail server and second is the domain name of the email address, from which it is being sent. That is your from-address.

While creating a good customer engaging content is one part of the story. But at the same time, sending emails to the relevant and verified user is equally important. And not following the email best practices might get you blacklisted. 

Sending emails with a blacklisted domain may result in reduced email delivery rates. Most global mailbox providers like Gmail, Yahoo, and Outlook drop emails coming from a blacklisted sender domain and assign a negative reputation score.

In this tutorial, you will learn A-Z of email blacklisting and how to get your domain and IP off the list.

FAQ

• What is an email blacklist?
• Types Of Email Blacklist Services
• Email Blacklist Categories
• Who Influences The Email Blacklist?
• How does DNSBL work with the MSP and ISP?
• What Are Some Signs Of Being Blacklisted?
• Check Domain Blacklist In Real-Time
• How Do I Know If My Emails Are Blacklisted?
• Behavior That Gets You Listed In Email Blacklist
• How do I get my email off the blacklist?
• How Do I Stop Being Added To Email Blacklist?

What is an email blacklist?

An email blacklist more known as DNSBL (Domain Name System-based Blackhole List) or RBL Real-time Blackhole List is large a list of public domains and IP addresses that are marked to be suspicious for sending spam emails over the internet. Organizations like Email Service Providers (ESP), Internet Service Providers (ISP), and Anti-spam agencies (ASA) refer to this list to detect and block any spam emails entering their network. 

DNSBL or email blacklist list is not a single centralized list on the internet. However, many anti-spam organizations are maintaining their independent DNSBL list. Some of these lists are free to use while few require commercial licenses. 

Now you might be wondering what are these services and where to start looking? Well, let me tell you that there are two kinds of email blacklists out there.

Types Of Email Blacklist Services

There are basically two kinds of Email Blacklist services depending upon how are they available to the service using it. Let us find out what they are.

The third-party Email Blacklist Services

These are independent organizations that provide blacklists as a service to email services such as Gmail, Yahoo, Email delivery services, Spam engines, and much more. These are more widely available and open for public usage, to freely check their listings manually.

If you want to get started with the blacklist check, we have listed some of the most popular email blacklist check databases that you should definitely start with.

List of Popular Email Blacklist Check Databases

For checking your domain listing in the blacklist database here are some of the most popular ones you can look up your IP or domain name in:

• Composite Blocking List (CBL)
• Senderbase
• Spam and Open Relay Blocking System (SORBS)
• Spamhaus Block List (SBL)
• XBL Exploits Block List
• Spamcop
• Passive Spam Block List (PSBL)
• Invaluement
• Barracuda
• SenderScore

Most of these blacklist databases of IP addresses and domains also include the addresses of known spammers, open SMTP relays, proxy servers, and zombie computers that are compromised by hackers and malicious code.

The Internal Email Blacklist Service

Although Gmail, Yahoo might use these third-party services to check to blacklist, they also have their own filters to update their version of blacklists. These internal blacklists are not so much as open to the public users to use without any verification.

These services store blacklists in different categories. Let's check them out.

Email Blacklist Categories

An email blacklist is divided into two categories depending upon what identifier is used to identify the spamming source

• IP Blacklist - Every server has an IP address that defines its location on the internet. As for your emails, they are sent from an email delivery service to be sent to the receiving services such as Gmail. The public IP address of the servers that are known to send spam emails / that are infected with botnet / servers that are acting as an open relay are mostly added to the IP blacklist.

• Domain Blacklist - Every email that you send has a domain associated with it, this domain is called an email sending domain. This domain can be seen in From-address, Return-address, and Also in DKIM signing domain.

If emails that are sent by these domains are considered to be spam emails based on the sending habits and history of email sending, they can be added to the email blacklist.

What now?

Now we know what are the different services that provide email and IP blacklist. So? let's move on to checking and removing your email from the blacklist, Right? No.

Permanently removing your email from the blacklist consists of more things than just blatantly ask for removal and delisting your email from the blacklist. Try it, and you will be listed again.

For you to be able to solve your email blacklisting problem, you need to know why that happens and what are the identities and services that are responsible for your domain or IP being listed into the blacklist. So let's move to blacklist authorities, entities, and influencers that are responsible for adding you to the blacklist and how can they do it.

Who Influences The Email Blacklist?

You might be sending very good quality emails, but even a small mistake can make your domain blacklisted. For example; if your list is not opt-in, and it is procured from some external source, then there is a high chance of your list containing spam trap (honeypot) email addresses. Hitting spam trap email addresses will lead to an immediate blacklist of your sending domain and IP address on multiple DNSBL services. 

MSPs, ISPs, Anti-Spam vendors, and even the normal recipient user of your email can influence the blacklisting of email sender domain or IP address. Let’s understand these scenarios one by one.

The Mail Service Providers (MSP)

MSPs are the email services that provide you with email inboxes like Gmail, Yahoo mail, Outlook, Zoho Mail, and so on.  These services are in a constant lookout of the suspicious emails and will spare no one if they find the emails being spammy let it be ESP or an individual. They use multiple resources to filter spam emails namely: Anti Spam Engines, Third-party Email Blacklists, Domain Reputation List, and Email Policies that define how they will behave against certain types of emails.

The Email Recipient

These are passive influencers in the email blacklisting. The open SMTP protocol allows the sending of any kind of email to any of the recipients, and there is no protocol-level check or restriction. Despite having a lot of anti-spam software in the industry, it's tough to catch and hold all sorts of spam.

To avoid spam, most MSPs provide a button such as “Report as spam”, which is like open polling, and if there are enough flags raised against your email, then there is a very high chance of your domain getting added to the blacklist.

Spam Traps or HoneyPot Email Addresses

These are the email addresses that appear just like an ordinary email address, primarily owned by the anti-spam agencies and MSPs. They distribute these trap email addresses across the internet to check if someone is sending emails on non-opt-in users. Most of the harvested/third party email list consists of a few spam trap email addresses. Hitting even a single spam trap can influence the real-time blacklisting on your sender domain and IP address.

Even though there are a lot of different types of Spam Traps, they are mainly categorized into two base categories.

1. Classic Spam Traps: The email ids are the ones that are primarily created to basically blacklist anyone who sends emails to these email id.
2. Recycled Spam Traps: These are basically email ids that are abandoned or unused for a long time or just closed accounts, mostly used by ISP. These are less strict on adding you to blacklist but will certainly damage your domain reputation.

A Sudden Increase In Email Volume

This is a common mistake that almost all new marketers do. Shooting up of your email volumes is an alert sign that you are sending emails to an email list you didn’t build on your own but have acquired it in bulk from some external source. Simple logic- How come you got so many subscribers in a single day?

With that said, the industry is now in more control of the email blacklist than you can ever think. They are using DNSBL services and even have their own rules for blacklisting.

The DNSBL service is not just a constantly updated directory of domains, but more of a software environment that works in close conjunction to the ISP’s DNS (Domain Name System) that is responsible for mapping your IP address to Domain name and vice versa. 

Is that a need to worry? We have just looked at a scenario when you are listed on the blacklist but not how it is seen by multiple services that use it.

Now with your domain/IP being blacklisted, does everything stop? Can you only send emails after being delisted? it depends. To answer that question we need to look at how the MSP and ISP (Basically all of the internet mailing services) work with DNSBL and deal with emails from blacklisted domain and IPs.

How Does DNSBL Work With The MSP and ISP?

Every MSP and ISP uses one or more DNSBL services to identify blacklist emails. They either set these services locally or use them through a remote connection. Either way, the DNSBL service uses the local DNS server to map through the domain IP to identify the emails into the list. This helps MSPs to catch hold of the incoming spam at the entry MX level itself, protecting the entire infrastructure and surely the recipient’s mailbox from receiving spam. The MX server generally drops these emails and sends a bounce email back to the sender address based on server policy. Which we will be discussing next.

What Are ISPs Email Policies

Each ISP and MSP on the internet mostly have their proprietary algorithms on how they want to deal with the email spams. It is not necessary that if you are unable to deliver emails to a particular MSP say gmail.com; then you also won’t be able to deliver to another MSP say yahoo.com.

Few immediately blacklist the sender and start discarding the email with a specific bounce reason code, while few others don’t blacklist but just drop with a bounce code.

It's important to act on incoming bounce notifications in real-time. Different bounce reasons require a different level of efforts at your end;

1. If the bounce is around blacklisting, then you might have to suspend your email programs and relook into the email list and what you were sending.
2. If the bounce is around email throttling, then you might be slowing down your email sending speed. 
3. If the bounce code is tagged as hard, then in such a scenario you should be removing the associated email address immediately from your list. 

The industry believes in fighting spam together, and this is precisely why MSPs and ISPs are most of the time open to sharing reasons for bounces. Not taking immediate action on these bounces, signals the authorities of you not being compliant with the email sending guidelines. 

Here is a flow diagram to explain the email filtering procedure followed by many email service providers to filter blacklisted emails.

In this diagram, you can see that the sender IP is matched against the blacklist, and based on the response and policies different actions are performed:

• The message is rejected and bounced back to the sender address with notification
• The message is accepted to the inbox

The policies for email filtering depend upon the internet service that is actively doing the filtration. Let us see these in detail.

How ISP Use Their Internal Email Blacklist

Every email service provider including Gmail, Y-mail, and Outlook has a domain reputation list that would mark you as a good or bad sender based on your email activity and would use your domain reputation to decide your email eligibility to be delivered to the inbox. Take an instance of Gmail, they provide a tool called Google-Postmaster in which you can check your domain reputation. Based on the domain reputation action on the received email is decided by the Gmail ISP.

We all know that there are many ISPs other than google and they too have their reputation list and blacklist, but right now you will only get notifications regarding emails being dropped as warnings. These services haven't kept their reputation list to be checked and accessed by the public right now, but you can expect it in the near future.

You can see those warnings if you send your emails to yourself and check the email.

Getting listed in the ISP's own blacklist sometimes can a lot problematic than being listed in the third partly RBLs, mainly due to strict policies they use to filter spams and they don't go easy on emails who don't comply with their email policies. Mailbox services such as Gmail, Yahoo, Outlook are one of the largest MSPs and provides inboxing to most of the number of people in the world, so you want to be on the good side of these services.

Gmail Spam Filter
Outlook Spam Filter
Yahoo Spam Filter

What can we conclude from the above discussion?

Now you know that not every blacklisted email is discarded immediately by every ISP is a bit of relief. But still getting blacklisted is still not a thing to take lightly. When a service decides by its policy to block or drop your emails then you will experience delivery problems and could make your emails identified as spam by other email services.

So let us now move forward to the first step. Identifying that you have been blacklisted. When you are indeed blacklisted by any Email Blacklisting service or a mail service provider you will normally receive a notification through email or bounce email to your return address.

But if for some reason you have not able to receive these messages and are facing difficulties you can check some of the subtle signs that could mean that you are blacklisted. This is discussed in detail in the next section.

What Are Some Signs Of Being Blacklisted?

If you are blacklisted, you won’t be able to send emails to the recipient’s mailbox properly. Most of the time, it can be dropped at the recipient’s MX server giving you a bounce code. But does that mean you will entirely be blacklisted from every mail server in this world? No.

Even if you are blacklisted on a particular DNSBL service, there are hundreds of other email blacklists on the internet. Non-delivery of your email completely depends upon whether the recipient’s server is your case, is referring to that particular DNSBL or not where you’re blacklisted.

In another scenario where the MSP/ISP is not using the blacklist that you are listed on, then there is a high probability of your sending domain or IP address won’t getting marked as a suspicious spammer. However, you have to understand that MSPs can have other email filtering mechanisms to filter out spam emails other than blacklists.

For example, few MSPs consider your past emailing history and engagement on those emails as the key parameter to classify or reclassify your domain/IP as blacklist too.

To Summarise here are some instances that show you might have a problem with your domain or IP being added to an email blacklist.

• An increasing number of Emails being dropped.
• Deteriorating Delivery rates
• A high number of Email bounce rates

But these are not enough to confirm you being blacklisted, just some warning signs. With clear signs of delivery issues and some drastic drops in email delivery, we can now move forward to check and confirm the blacklisting of domain or IP address. You can use the provided tool below to check your email in the blacklist, or you can continue with the process in the next section.

Check Domain Blacklist In Real-Time

Server IP or Domain

The blacklist check will scan an IP address or domain against over 200 DNSBLs or RBLs. If your domain or the mail server's IP address has been blacklisted, there is a high chance that some of the emails you send may not get delivered. If you don't know the IP address used for sending your mails, then check the email headers of few sample emails to get an idea or just write to Pepipost Email Expert at dx(at)pepipost(dot)com

How Do I Know If My Emails Are Blacklisted?

Now is the time to confirm your listing in the third party blacklists services. But where to check? One of the ways is to check some of the obvious signs that you are blacklisted, just as mentioned in the "What Are Some Signs Of Being Blacklisted?" section.

There are two ways you can identify your blacklisting, they are as follows.

Bounced Emails

The worst turn your domain or IP being blacklisted is that emails might get dropped and bounced. If you are worried about this, don't be, and check your bounce back emails. Most of the big blacklisting services and ISPs provide SMTP error codes on the bounce back emails so you can understand the reason for being listed into the Email blacklist. You can identify based on the SMTP error codes why the emails were blacklisted in the first place.

Some services like Spamhaus provide a panel where they show you all of the SMTP errors from your domain. To check that out you first have to signup for their services, which is free. There you can check the status and reason for your emails being dropped by checking their SMTP error code table. If this is too much hassle, you can also check these SMTP errors in your email servers log.

Some examples of Bounceback emails from ISPs

Here are some of the examples of SMTP message logs for Yahoo, Gmail, and Outlook. These are the ones that are due to being internally listed on their blacklist but not on any third-party email blacklists.

Yahoo!

August 16 17:38:04 messagerie-prep postfix/error[12137]: 54B5B64010C:  to=<[email protected]>, relay=none, delay=17397,  delays=17397/0.02/0/0.03, dsn=4.4.1, status=deferred (delivery  temporarily suspended: connect to  mx-eu.mail.am0.yahoodns.net[188.125.69.79]:25: Connection timed out)

August 16 17:43:09 messagerie-prep postfix/smtp[12502]: BFC8564010F:  to=<[email protected]>,  relay=mta6.am0.yahoodns.net[98.136.101.117]:25, delay=1128,  delays=1123/0.08/4.5/0.23, dsn=4.7.0, status=deferred (host  mta6.am0.yahoodns.net[98.136.101.117] said: 421 4.7.0 [TSS04] Messages  from 197.201.1.54 temporarily deferred due to user complaints -  4.16.55.1; see Error:  "421 4.7.0 [XXX] Messages from x.x.x.x temporarily deferred due to user  complaints - 4.16.55.1" when sending email to Yahoo

Gmail

August 13 11:07:09 messagerie-prep postfix/smtp[11924]: 4E415641FD5:  to=<[email protected]>,  relay=gmail-smtp-in.l.google.com[173.194.76.27]:25, delay=4.7,  delays=0.06/0/0.41/4.3, dsn=5.7.1, status=bounced (host  gmail-smtp-in.l.google.com[173.194.76.27] said: 550-5.7.1 [197.201.1.54       19] Our system has detected that this message is 550-5.7.1 likely  suspicious due to the very low reputation of the sending 550-5.7.1  domain. To best protect our users from spam, the message has been  550-5.7.1 blocked. Please visit 550 5.7.1  Why has Gmail blocked my messages? - Gmail Help for more information. 91-v6si6257010wrg.38 - gsmtp (in reply to end of DATA command))

Outlook

August 16 16:39:06 messagerie-prep postfix/smtp[8006]: 346B56400E6:  to=<[email protected]>, relay=none, delay=260903,  delays=260840/0.01/63/0, dsn=4.4.1, status=deferred (connect to  eur.olc.protection.outlook.com[104.47.6.33]:25: Connection timed out)
May 16 16:48:33 messagerie-prep postfix/smtp[8708]: connect to  eur.olc.protection.outlook.com[104.47.14.33]:25: Connection timed out

Checking your IPs and Domains in Email Blacklist Directory

If you think to check your email blacklisting in the 10 or so RBL service is enough, then you are wrong. There are hundreds of different kinds of email blacklist services on the internet. Checking manually in all of these services isn't a practical solution and will take days to check in all of them, considering you do know all of the services.

To save your precious time there are services on the internet that maintains a list of live RBL directories to lookup your domain/Ip address and check if you are listed or not. They even provide a page dedicated to that particular RBL service detailing types of RBL list they use and some links to help you delist your domain/IP address.

Here is a list of the popular lookup tools to check the domain blacklisting on various DNSBL lists:

MultiRBL: This is a free DNSBL lookup site that scans on 100+ DNSBL lists to check for domain blacklisting. It also shows the details regarding the listing and steps to remove your domain from the blacklist.

MXToolBox: Similar to MultiRBL, MXToolBox is another tool that checks for blacklisting of your domain in multiple RBL List. And it too provides detailed info for the blacklisting. MXToolBox also provides suggestions on your domain's current status and blacklisting.

There are many others, but these are the ones you can get started to monitor your blacklisting status continuously. Then you can go forward to research many other prominent services you can find to add in your list the more, the merrier.

Third-Party Blacklists:

You can also check into the individual lists of RBL services such as Barracuda, Spamhaus. They will give you more detailed information about listing.

These are some screenshots for Spamhaus Blacklist

Ok, you have found out that you are indeed listed into the DNSBL list and you want to remove your domain or IP immediately from the list. Should we do that next? Well, hold on. Before you request delisting of your site you must fix the issue that got you listed in the first place. The next section deals with this.

Behavior That Gets You Listed In Email Blacklist

If you want a clear explanation of what was the problem that got you listed. These are some RBL services that provide that information when you do a lookup into their RBL list as shown in the example of the Spamhaus CBL blacklist lookup page below.

With that, here are some of the common issues that would be a reason for your blacklisting.

Email Content

Email content might be one of the main reasons for the email blacklisting is the Email content which includes

• Spammy Title, that clearly miss represents the content.
• Spam words in content like - Buy Now
• Full caps words in content - GREAT OFFER
• A misleading Subject line which clearly leads users to believe what is actually is in the email body.
• HTML content size and structure - Using links and images in a really bad way and not maintaining a clean HTML structure

To know more about Email content check out our article on Email Content Best Practices.

CANSPAM-ACT

Canspam-act is basically a rulebook defining how you should send emails and what are the necessary components of sending emails. If your emails don't follow the can spam act then they are more likely to be marked as Spam.

Virus, Trojan or Spambot infection

A system Infected through any malware might be doing the email activities that are not good for either your server or your domain reputation. This infector malware does their job secretively and if you are not carefully monitoring your system, they might wreak havoc on your system. It is anyone's guess that you will be blacklisted or blocked for this kind of email activity. Always maintain a clean system by regular antimalware checkups.

Also If you are infected with Spambot then you might be basically unintentionally involved in email harvesting and might be considered as a sender to avoid, so more email drops.

Open Relays

If you are using any free services to send emails through open relays (basically the email server that allows sending emails through them without any verification) you will get into trouble. Spammers use these servers to send emails and you might get mixed up into their email behavior. To stop this use some reputed paid service that will save you a lot of hassle.

Email List Hygiene

It is recommended you remove these kinds of emails from your email list:

1. Non-active emails: Usually these emails that never open or never interact with the emails you have sent. Also, they are potential spam traps.
2. Invalid emails: Invalid emails are the causes of hard bounces and a freeway, towards a low domain reputation leading to email blacklisting.

How Do I Get My Email Off The Blacklist?

• If you’re managing your email delivery, then check your return path/abuse mailbox, if your domain is on the blacklist. You might have got an email regarding the blacklist from the DNSBL list owner and a link to delist your domain name from the service.
• If you’re using some Email Service Provider (ESP) like Pepipost, then contact them to help your domain to get removed from the blacklist.
• Some RBLs automatically do listing and delisting according to the last blacklisted time. That means if you have been listed on their blacklist, they wait for a certain duration of time to delist your site automatically. This is works only if there are no repeated listing made on your IP in that particular time duration. The time duration to delist can defer depending on the service. So what you want to do after being listed is to stop the emailing activity entirely and resolve the issue that got you blacklisted in the first place. After the issue being resolved, you will be automatically removed from the database If you are not listed again.
• You can also directly contact the blacklisting service through email.
• The domain blacklisting services mostly have a delisting form in case you want to delist your IP or domain from the blacklist. Just fill in the form with your domain name and contact details and a valid reason for delisting. The reason should be that whatever scenario that has got you blacklisted has been fixed.

Note:- You should make a delisting request to the blacklisting authority, only if you have fixed the problem that got you listed in the first place. Not doing so will land you in the blacklist again even after you are delisted once.
Also, please remember that some of the blacklisting services will not allow you to delist your domain/IP if you are being frequently listed and delisted too many times. So make sure to clean your act before the delisting request is made.

To summarize this here are the simple steps that you usually have to take for delisting of your IP / Domain address.

1. Lookup into the DNRBL or MULTIRBL site for your Domain / IP address.
2. After you found yourself to be listed, check the recommendations provided by the RBL or Multirbl site.
3. Fix the issue that was the cause of your listing in the email blacklist.
4. Request a delisting through a Delisting Form or through a direct email to the listing service.

With all of your hard work and research, you have now successfully removed your email from the email blacklist. But, can we all just stop here and guarantee that you won't be blacklisted in the near future? The answer is No. You can take precautionary measures from now on, to avoid getting blacklisted in the email blacklist again, Some of them are listed in the next section.

How Do I Stop Being Added To Email Blacklist?

Prevention is a continuous process and it will never stop. Why? because preventing yourself from being added to the email blacklist is a habit you need to make yourself follow while you are sending bulk emails be it marketing or promotions. Here are some of them we have listed for you to begin with, and direct you in developing good email delivery habits.

1. Avoid procuring lists from external sources: 92% of the purchased list from external sources consists of spam traps. And as discussed, above in the tutorial, these spam traps are the leading influencer for your domain or IP to get blacklisted.
2. Send emails to opt-in user list only: Make a practice to add users through self-initiated subscriptions.
3. Remove inactive or bounced email addresses from your regular mailing list: Not acting on bounce email notifications is a clear sign of a company not following the email sending guidelines and are bound to get flagged as blacklisted by either the MSPs or ISPs.
4. Respect un-subscribers, don’t retarget them: Sending emails to unsubscribed users will lead to an increase in Spam Complaints. And, an increase in such patterns will ultimately lead to email blacklisting.
5. Avoid a drastic increase in mailing volumes:  Instead, increase it steadily and gradually. Sending irregular patterns of emails is a clear sign of a company sending emails on a purchased third party list and which in turn raise alarms at the MSPs level. Follow the email warmup process before sending emails at scale.
6. Create Smart segments to target users: Carefully choose your target audience, narrow down their categories, and send emails accordingly. This means taking the time to plan and design your campaign for all user groups you've targeted.
7. Don’t sell, instead create values: Avoid email content that sounds like forced marketing innuendo or direct marketing.
8. Fortnightly monitor your domain and IP reputation: Monitor the reputation of your domain and IP on various tools like MXToolBox, MultiRBL, and few more suggested in this guide.
9. Don't send emails through an open relay SMTP server: Open relay SMTP server is an email server that is open for all people to use without any authentication. Understandably, any spammers use these email SMTP relays to send a bulk of spam emails which is quite bad for you if you are using the same SMTP relay server.
10. Create your email content to look less like a Spam mail: With marketing emails everything from the user content. Things like email body structure, email size, and email text define how your email is being perceived by spam engines. This is fairly important and even if you follow all good practices with emails sending, a bad email can land you in spam easily.

Conclusion

I hope the information is helpful. In case you have any queries related to your domain blacklisting, then please feel free to comment below or reach out to the Pepipost Deliverability Expert Team at dx(at)pepipost(dot)com.

Other Related Tutorials.

Spam Traps

Email spam

Email Bounce

Domain reputation

barracuda blacklists

spamhaus blacklist

cbl blacklist

email content best practices