What is a blacklist?
Technical support

What is a blacklist?

Blacklists (also called blocklists) are a collection of IP addresses that have been identified by Internet Service Providers (ISPs, such as Google or Outlook) as being responsible for sending spam.

In other words, IP blacklists are anti-spam tools designed to prevent unwanted mail from being sent. If an IP address is blacklisted by an ISP, it means that the ISP has flagged the sender as a spammer. It seems easy to understand, therefore, why getting blacklisted is one of a marketer’s biggest nightmares?

Not only can an IP address be blacklisted, but so can domain names. This means that even if we send our emails from a different IP, our emails can still be picked up by these blacklists, which will prevent our messages from reaching their destination.

What is the difference between a blocklist and a blacklist?

Actually, none. Blacklist and blocklist are terms used in English to refer to lists of email addresses that Internet providers recognize as spam senders, what we usually know in English as a blacklist.

In recent times, the use of blocklists and other Spanish terms such as “listas de bloqueo”, “listas de exclusión” or “listas de direcciones que envían spam” has become more widespread as part of a broader effort by the technology industry to adopt more respectful and inclusive language.

Why is my IP address or domain name on a blacklist?

There are several reasons why our IP address or domain name may end up on a blacklist.

Sending unwanted emails

First of all, there is the most obvious option: that we are sending spam to our contacts. If many of our contacts send our messages to the spam folder, the ISP or mail servers (Gmail, Hotmail, Yahoo…) will notice and we face the risk of being blacklisted.

Sometimes, it is not that the content of our messages is directly junk mail (although certain words can trigger spam alarms), but that we are sending emails to people who have no interest in receiving them, for example because we have purchased a contact list. This can lead them to mark us as fraudulent senders and jeopardize our deliverability.

Victims of phishing

Another reason why we can end up on a blacklist is because we have been victims of what is known as phishing or identity theft. Sometimes, our email accounts can be hacked and our email address used to send spam without us realizing it. Therefore, if we suspect that messages are being sent in our name, it is advisable to clean our computers from malware that may be taking control of our account.

IP marked by mistake

There are also occasions when our IP address falls into a blacklist because it is in the vicinity of others that do in fact send spam. In some cases, not only the IP address responsible is blacklisted, but also multiple similar IP addresses are blacklisted. Other times, our IP address is in a blacklist database because the previous user of that IP made fraudulent use of it.

Changes in spam rules

However, sometimes we get blacklisted due to factors beyond our control, such as a change in spam policies or ISP security algorithms. In these cases, even the most careful senders can end up being affected, so it is important to follow the tips we offer to keep your mail safe.


How do I know if I am on a blacklist?

If we suspect that our email is not getting through, the first thing to do is to check that our IP address and domain name are not on a blacklist.

There are numerous blacklists, although most ISPs use the largest and most reputable lists, such as Spamhaus, DNSBL, or Spamcop. To check if you are on one of them, you can use sites such as Blacklistalert.org, MultiRBL.valli, or MxToolBox to do a blacklist check. There, by simply entering your IP address or domain name, you can see your status on a large number of blacklists.

What can I do if I am on a blacklist?

If indeed our information is in the databases of a spam blacklist, we will have to contact the administrators of the different lists to ask to be deleted. This is not always easy, so when it comes to blacklists, it is always better to be safe than sorry.

One of the benefits of our integrated technical support offer is to monitor and help you prevent your IP from being blacklisted, and at the same time, correct your mail server configuration problems. It is much cheaper to pay a small monthly fee by contracting our service than to be unable to deliver emails because you are blacklisted.

How can I avoid being blacklisted?

If your IP address or domain name is not blacklisted, or you have managed to get it deleted, congratulations! Now, you just have to avoid being blacklisted again. And to do that, you need to know (and follow!) good practices in deliverability and email sending.

We’ve written some tips specific to blacklisting that can help you:

  • Ask users to add you: Getting your customers to add your sender address to their address book increases your deliverability, as ISPs will see you as a personal contact of this individual customer. Also, this way, your emails will stay out of the promotions tab and in the inbox.
  • Do not use link shorteners: Link shorteners can be extremely useful for shortening long URLs, but they can be detrimental in the eyes of an ISP. These shortened links mask the original URLs, which helps spammers hide the URL used in their CTAs, for example. Not all blacklists take this into account, but it is always safer to stay away from shortened links.
  • Manage unsubscribes: Regularly manage your contact list to ensure that it is up to date and that all unsubscribes and bounces are removed from the list. Sending emails to customers who have unsubscribed damages their trust in you and affects your deliverability.
  • Monitor your blacklist status: Another important point is to regularly monitor your blacklist status and your sender reputation. Once a week, use sites like Return Path to check your IP address in these databases to make sure you are not blacklisted.
  • Stay up to date on spam trends: ISPs continually refine their anti-spam algorithms to combat spammers’ attempts. Although we cannot know exactly what changes they implement, it is always advisable to keep up to date on the latest trends in deliverability, spam, and security issues.

How can Dofleini help me?

To avoid these deliverability problems and help our customers, at Dofleini we provide an integrated technical support offer service in which our team of experts works on a monthly basis to manage the reputation and deliveries of our customers and shared IPs. In this way, we help companies comply with the necessary regulations to avoid being blacklisted and, at the same time, we advise on the correction of all problems in their IT ecosystem.

At the same time, we maintain a very close relationship with ISPs, which allows us to manage and prevent problems like this one, which can affect our clients’ emailing strategy. This allows us to offer our users first-class deliverability and support.

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