What is Blacklist – Learn How It Works


Blacklist is the lists with those that practice more spam. However, some legitimate senders fall into these lists for basic errors. Learn what to do to avoid this situation.


A practice that holds back abuse

Internet companies and independent initiatives are the major creators of the blacklists, aiming to combat spam.

The access to these lists can be charged or offered for free.

At first, anyone can create their blacklist by combining data from various public lists as well as data from their networks to determine the credibility and reputation of a particular sender.

It is important to note that blacklist providers are not solely responsible for blocking; the inclusion of the senders in the blacklists usually occurs for the lousy quality of lists of contacts and for denunciations of who received the email.


The basic operation of a blacklist

There is a maximum number of spam notifications and blacklist listings that are tolerated by email providers. These spam notifications also called reports, typically use to bait emails called spamtraps.

And how does a spamtrap come? It looks like this: remember that email you had 5 years ago and never used it again?

This email can be reactivated by the provider to behave like a bait to spammers. Anyone who submits to this email gets caught in the trap and falls on a Blacklist. So it’s not a good idea to use old lists.

Spamtraps work as a security alarm for the provider, from which a certain sender is sending unsolicited email.

These spamtraps accounts are meticulously monitored, and when the provider receives a certain number of emails at this fictitious address, the sender’s email domain and IP are saved and added to an email blacklist.

The e-mail provider will use this information to determine the reputation of each sender who will send e-mails to him again.


Clarifying some terms:

 IP address:

The IP address means for the internet, just as the Zip Code implies for Canada Post. They represent the address of a device on the worldwide network.


They are informal names of devices on the internet, which, like streets and avenues names, serve to make it easier to identify a location. Domains represent IP addresses or technically speaking, direct to IPs.


It is an expression that refers to a data traffic that is captured and is not sent or passed on.


It is the standard way of locating a resource (file, service, media) on the internet or your computer.


Blacklists Types

There are currently two types of blacklists: the Unified Resource Identifier Blocklist (DNSBL URI) and the Real-time Blackhole List (RBL or IP DNSBL)


Based on an IP or Domain

The Real-time Blackhole Lists (RBL) and DNS-based Blackhole Lists (DNSBL) are lists with IP’s and blocked domains and are updated in real time.
E-mail message header data, such as the sender used, and the infrastructures from which the sending originated, are analyzed through this type of list.

In addition to identifying Spammers, this type of list is used so email providers can also check if the person responsible for sending the message allows irregularities. Such as open relays, where anyone who connects can send emails from its structure, or those that would enable you to forge senders using an email that is not part of your domain.


Based on URI

The DNSBL URI lists the domain names and sometimes also the IP addresses that are found in the clickable links and the images contained in the body of the spam but are not typically found in the legitimate messages. It is a protection that helps a lot in cases where the spammer has switched to a new IP or domain that has not yet been listed in RBLS.



Your IP or Domain has been blocked, now what?

When the sender that you use is blocked in some way, you must immediately request the removal from the agency or company responsible for the list. However, doing this over and over can cause reputational issues, and whoever manages these lists will ignore your removal requests. First of all, it is necessary to take measures that eliminate the causes of the block, before asking for the removal of your IP or domain from a blacklist.

And what can happen?

When your IP or Domain falls into these lists, your messages may no longer be accepted by multiple email providers for a period of time.

If the service you offer depends on emailing payment invoices or transactional emails, this is a terrible situation, and it will undoubtedly cause you losses.

Depending on the entity that manages the block list, the release can take several days.



3 required steps to avoid blocking your email submissions

Our tip is to follow these basic recommendations to address the situation if it happens, but mainly to prevent it, if possible:

1) Set up SPF and DKIM correctly:

SPF is a technology that aims to combat the unauthorized sending of messages on behalf of a particular domain, and DKIM uses a public key structure to ensure the authenticity of its sender.

Check out the blog material on the subject:
The Importance of SPF, CNAME, and DKIM to improve deliverability
Why did my email arrive as spam?


2) DMARC configuration

With the correct DMARC setup, it is much simpler and more efficient to determine if a message is legitimately sent from a purported sender; but not just this: DMARC allows you to define what to do if the message is not from the sender.

3) NEVER EVER buy contact lists. Do not even use other lists.

Have your email list base. The sending of e-mail to those who did not request it is a practice of spam. Soon, the purchase of lists is already considered spam, because you will be sending to contacts that do not even know if they exist, they may have become SPAMTRAP, and you can not tell if they are valid contacts.

Bonus Tip:

Check the situation in fact: periodically use tools like multirbl.valli.org or mxtoolbox.com detect if your domain or IP is blacklisted, go here