Blocklists, also known as blacklists, are crucial tools in cybersecurity, particularly in the domains of spam blocking and threat intelligence. They are used to prevent unwanted emails, reduce the risk of network attacks, and manage internet abuse by listing IP addresses, domains, and other identifiers associated with malicious activity. The choice of which blocklists to use can depend on the specific needs of a network, its traffic patterns, and the types of threats most commonly faced. The reasons you might need a blocklist are covered in this previous article, but here are some of the most important and widely respected blocklists in the world:

1. Abusix Mail Intelligence

Importance: Abusix Mail Intelligence provides dynamic, real-time blocklists that help protect against spam, phishing, malware, and other email-borne threats. It is particularly known for its accuracy and the rapid updating of its lists, which are based on a combination of automated data collection and community feedback. This makes it a highly responsive tool in the face of emerging threats. These lists are used by many large ISPs and corporations.

Recommendation: Due to their reliability and broad acceptance, Abusix blocklists are highly recommended for most organizations, especially those dealing with large volumes of email. Abusix Mail Intelligence is well-suited for organizations that need a highly reliable, real-time solution to protect against a wide range of email threats. It’s particularly beneficial for companies in dynamic threat environments where new threats can emerge quickly. It can be a critical component of an integrated security system, especially in environments where email is a common attack vector.

2. SURBL

Importance: SURBL is focused on blocking URLs linked to malicious activity. It is used to complement traditional IP address blocklists by identifying and blocking harmful links embedded in emails. This approach is beneficial for preventing phishing attacks and other forms of social engineering.

Recommendation: SURBL should be used alongside IP-based blocklists to enhance email security, particularly if your organization faces risks from phishing and malicious URLs.

3. SORBS (Spam and Open Relay Blocking System)

Importance: SORBS maintains a variety of lists that identify spam-sending servers, open relays, and other potentially harmful internet resources. It’s a comprehensive tool for organizations that need detailed control over their incoming traffic.

Recommendation: Consider SORBS if your organization requires a more granular level of control over email and network security, though be mindful of the potential for false positives, which are higher with more comprehensive lists.

Editor’s Note: SORBS is reportedly being shut down

4. Barracuda Reputation Block List (BRBL)

Importance: Well-regarded for its effectiveness, the BRBL is provided by Barracuda Networks, a prominent security company. It offers a robust list of IP addresses known to send spam, and it’s maintained with updates based on data from Barracuda Networks’ extensive customer network.

Recommendation: The BRBL is a good choice for businesses looking for a reliable, regularly updated service with strong support.

5. Spamhaus Blocklists

Importance: Spamhaus blocklists are some of the most known in the world. They are known for their comprehensive coverage of spam-related IPs and domains. Spamhaus operates several lists, including the Spamhaus Block List (SBL), Exploits Block List (XBL), and the Policy Block List (PBL). These lists are effective at reducing inbound spam and are used by many large ISPs and corporations.

Recommendation: Spamhaus blocklists are recommended for many businesses that deal with large volumes of email.

Factors to Consider When Choosing Blocklists:

• Accuracy and False Positives: Evaluate the potential for false positives, as overly aggressive blocklists can block legitimate communications.

• Specific Needs: Assess whether the blocklist caters specifically to the types of threats you frequently encounter.
• Maintenance and Updates: Opt for blocklists that are regularly updated to adapt to the fast-evolving nature of cyber threats.
• Cost vs. Benefit: Some blocklists are free, while others require a subscription. Consider whether the benefits provided justify the potential costs.

The Choice Is Yours

The choice of blocklists should be tailored to the specific security needs and threat environment of your organization. Abusix Mail Intelligence, Spamhaus, SURBL, SORBS, and Barracuda are all excellent starting points due to their credibility and widespread use. These tools are not just technical solutions but also components of the broader product and service offerings that can be integrated into your company’s portfolio to enhance overall cybersecurity defenses.