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Real-time Blackhole List

RBL, or Real-time Blackhole List, is a tool used in email management that acts as a real-time blacklist to identify and block IP addresses that are considered to be sources of spam.

These lists are constantly updated to reflect IPs that are sending large amounts of spam.

By using an RBL, mail servers can filter and reject messages from these addresses, thereby improving the quality of email reaching recipients.

Relevant historical data

The history of RBLs dates back to the 1990s, when the spam issue began to grow exponentially with the increase in email usage.

The first RBL was developed by Paul Vixie in 1997, known as MAPS RBL (Mail Abuse Prevention System Real-time Blackhole List).

This revolutionary tool allowed system administrators and Internet Service Providers (ISPs) to automatically block emails from IPs suspected of sending spam.

Over time, various organizations and technical communities created their own versions of real-time blacklists.

Some of the best known are Spamhaus, SORBS and Barracuda.

These lists have evolved to include not only IPs, but also domains and URLs that are considered to be sources of unwanted or malicious mail.

The evolution of RBLs has been instrumental in blocking spam and protecting email integrity.

Key considerations

For email marketers, understanding the workings and importance of RBLs is crucial.

Some key considerations:

  • Impact on email deliverability: if an IP address is listed in an RBL, email sent from that IP may be rejected by recipients’ servers. This negatively affects the deliverability rate of email marketing campaigns.
  • Constant analysis: it is essential to regularly check the IPs from which emails are sent to ensure that they are not included in any RBL.
  • Whitelist and blacklist management: in addition to using RBLs, professionals should manage their own whitelists (trusted IPs and domains) and blacklists (known spam sources) to customize email filtering.
  • Compliance with best practices: following email marketing best practices, such as obtaining explicit permissions from recipients and maintaining clean databases, can help prevent IPs from being listed on an RBL. In other words, good list hygiene and a permission-centric approach are essential.

Why it is important, advantages

The use of RBLs offers multiple advantages for both mail service providers and legitimate senders.

Some of these advantages are explained on our blog:

  • Spam protection: RBLs help protect end users from receiving large amounts of spam, which improves user experience and reduces the risk of phishing and malware attacks.
  • Improved sender score reputation: by avoiding sending mail from IPs listed in RBLs, senders can maintain a better reputation. A good reputation translates into a higher deliverability rate and a more positive relationship with email service providers.
  • Operational efficiency: email servers can operate more efficiently by filtering unwanted mail before it reaches users’ inboxes. This reduces the load on servers and improves overall performance.
  • Regulatory compliance: In many countries, data protection and anti-spam laws require measures to reduce spamming. The use of RBLs can help companies comply with these regulations.


In short, RBLs (Real-time Blackhole Lists) are an essential tool in the email and email marketing ecosystem.

These real-time lists help identify and block spam sources, improving email quality and security.

For digital marketers, it is critical to understand how RBLs work and how they can affect the deliverability of email marketing campaigns.

Staying informed and following best practices can help avoid the problems associated with blacklists and ensure the success of email marketing strategies.