Farewell to SORBS: a pioneering DNSBL shuts down after two decades

After more than two decades of service, SORBS (Spam and Open Relay Blocking System), a pioneering force in the realm of DNS-based blacklists (DNSBL), has officially ceased operations as of June 5, 2024: learn more about the rich history of SORBS, its technical intricacies, and its eventual decommissioning.

June 27, 2024

SORBS (Spam and Open Relay Blocking System) was launched in 2001 by Michelle Sullivan, a network engineer who sought to address the growing issue of spam and open relay abuse on the internet. At its core, SORBS was designed to maintain a blacklist of IP addresses known for sending spam or being open relays and these blacklists could then be used by email servers worldwide to filter incoming emails, blocking those originating from blacklisted IPs.

The SORBS (Spam and Open Relay Blocking System) system operated as a DNS-based blocklist, meaning that email servers could query the SORBS database via DNS to check if a particular IP address was blacklisted. The primary DNS endpoints used by SORBS included:

  • dnsbl.sorbs.net: This endpoint provided a comprehensive blacklist combining various categories of spamming and open relay sources.
  • http.dnsbl.sorbs.net: Focused specifically on IP addresses that hosted websites involved in spam activities.
  • smtp.dnsbl.sorbs.net: Targeted IP addresses that were identified as sources of spam via SMTP.
  • web.dnsbl.sorbs.net: Listed IP addresses of compromised web servers being used to send spam.

These endpoints allowed administrators to implement fine-grained spam filtering based on the specific nature of the threat.

SORBS' Evolution and Adoption

Over the years, SORBS gained significant traction, becoming one of the most widely used DNSBLs. It was embraced not only by hobbyist email administrators but also by larger organizations looking for an effective way to combat spam. At its peak, SORBS maintained a database of over 12 million blacklisted IP addresses, a testament to its extensive reach and influence.

Acquisition by Proofpoint

In 2011, SORBS was acquired by Proofpoint, a leading cybersecurity company based in Sunnyvale, California. This acquisition marked a new chapter for SORBS, as it became part of Proofpoint's broader portfolio of email security solutions: despite the acquisition, Proofpoint chose to maintain SORBS as a free and open-source service, allowing it to continue serving the community without commercialization.

The Changing Landscape of Email Security

As the years progressed, the landscape of email security underwent significant changes. Advanced spam filtering technologies and more sophisticated anti-spam measures were developed, often integrated into comprehensive cybersecurity solutions. This evolution meant that the reliance on traditional DNSBLs like SORBS began to wane, particularly among enterprise users who opted for more holistic security solutions.

By 2024, the operational and financial challenges of maintaining SORBS became increasingly apparent. As a donation-based nonprofit service, SORBS struggled to remain viable in an industry that had largely transitioned to enterprise-grade, commercially supported solutions. On June 5, 2024, Proofpoint officially announced the decommissioning of SORBS, citing the need to focus on more advanced and sustainable email security technologies.

The Impact of SORBS' Shutdown

The shutdown of SORBS marks the end of an era in the world of DNSBLs. While its decommissioning may not cause a major disruption in email delivery, it does symbolize a broader shift in the IT and cybersecurity landscape. The move from free and open-source projects to proprietary enterprise solutions reflects the changing dynamics of the industry, where investment in development and advanced features often comes at the cost of community-driven initiatives.

For those who relied on SORBS, there are still several alternative DNSBL services available, including Spamhaus, one of the most respected and widely used DNSBL services offering a range of blocklists for different types of spam and malware sources, SpamRATS, SpamCop and many others.

While these alternatives continue to serve the community, they often come with their own sets of features and capabilities, catering to the evolving needs of email security.

Looking Forward

As we bid farewell to SORBS, it's important to recognize the contributions it made to the fight against spam. For over two decades, SORBS helped countless administrators keep their email systems clean and secure and its legacy will undoubtedly live on in the memories of those who benefited from its service: thanks to Michelle and her team!

In conclusion, the decommissioning of SORBS is a reminder of the ever-changing nature of technology and the importance of adaptability in the face of new challenges. As we move forward, the lessons learned from SORBS' journey will continue to inform and inspire the development of future email security solutions.

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