What caused the widespread Barracuda IP blacklist issues in June 2019?

Key findings

• Widespread impact: The Barracuda blocklist issue affected numerous ESPs and their customers, leading to a significant increase in blocked emails across multiple networks.
• Unclear cause: Initial investigations by affected parties struggled to pinpoint a definitive root cause, with some speculating about MSRBL (Microsoft Spam Reporting Block List) or Barracuda's internal systems malfunctioning. Barracuda eventually attributed it to a "routine transient spike in blacklisted IPs" that normally goes unnoticed.
• High volume of listings: Some ESPs reported hundreds of IPs being listed, with one expert noting an 18,000% increase in listings over daily averages.
• Delayed and unhelpful support: Barracuda's support channels were criticized for slow responses and providing generic, unhelpful advice, initially only delisting a few example IPs per request.
• Automated system glitch: Evidence suggests an automated system within Barracuda's threat analysis process may have over-aggressively blacklisted IP ranges, possibly due to old or 'resurrected' block data.

Key considerations

• Proactive monitoring: Continuous blocklist monitoring is crucial for early detection of such widespread issues, allowing senders to respond quickly.
• Multiple delisting channels: When automated delisting tools fail, exploring alternative contact methods (e.g., direct email to `intent@barracuda.com` or Twitter support, as seen in this incident) can be necessary.
• Impact on shared IPs: Organizations using shared IP infrastructure (like many ESPs) are particularly vulnerable to broad blocklistings, even if their individual sending practices are clean. Our guide on troubleshooting Barracuda blocklistings for shared IPs offers more insight.
• Maintain strong sender reputation: While this incident seemed external, generally maintaining excellent sender reputation, using double opt-in, and regularly cleaning lists reduces the likelihood of being caught in such wide-net blocklistings. More on this can be found in a relevant article by Word to the Wise.

Key opinions

• Shared experience: Many marketers quickly realized they were not alone, with multiple ESPs (e.g., Sparkpost, Mailgun, Pardot) reporting similar widespread blocklisting issues on Barracuda.
• Unresponsiveness from Barracuda: A common complaint was the lack of immediate official communication or effective delisting mechanisms from Barracuda, forcing marketers to seek unofficial channels for help.
• Impact on campaigns: The unexpected blacklisting led to significant delivery disruptions, impacting ongoing email campaigns and potentially critical communications.
• Speculation on root cause: Marketers debated whether the issue was related to MSRBL.net problems, internal Barracuda filter malfunctions, or the re-activation of old, problematic IP blocks.
• Gradual resolution: While frustrating, many eventually saw their IPs delisted, often after multiple attempts through email or dedicated support channels, suggesting a queued processing or gradual system correction.

Key considerations

• Leverage community insights: During widespread incidents, communities like Email Geeks provide invaluable real-time information and shared strategies. Staying connected can provide a competitive advantage.
• Understand your infrastructure: Knowing whether you're on a shared or dedicated IP and how your ESP handles blocklistings is crucial. Learn more about unexpected IP addresses on dedicated IPs.
• Prepare for communication: Have a plan to inform customers about deliverability issues, especially when external factors are at play, to manage expectations and maintain trust.
• Review Barracuda's policies: Even though Barracuda's lookup page from 2015 might mention outdated practices like emailreg.org, it's still helpful to be aware of their general approach to reputation management.

Key opinions

• System malfunction suspected: Experts quickly identified the issue as a significant malfunction within Barracuda's systems, rather than isolated bad sending behavior.
• Poor communication: There was notable frustration with Barracuda's lack of transparent communication and slow, unhelpful responses to delisting requests via their standard channels.
• Unprecedented scale: One expert quantified the scale, reporting an 18,000% increase in daily listings, clearly indicating an anomaly that was not part of a normal threat analysis process.
• Resurrection of old blocks: Barracuda's internal explanation hinted at the accidental re-activation of older IP blocks within their system, which then led to unwarranted listings.
• Impact on deliverability: The incident underscored how a single, influential blocklist could drastically affect the deliverability of legitimate email traffic across numerous providers.

Key considerations

• Transparency from blocklist operators: The incident highlighted the need for quicker and more transparent communication from major blocklist operators when system anomalies occur.
• Effective delisting procedures: Even for legitimate senders, efficient delisting procedures are paramount. Our guide on managing senders during blacklisting offers relevant steps.
• Redundancy and reputation management: ESPs and large senders should consider strategies like IP diversity and robust reputation management to mitigate the impact of single-point-of-failure blocklist events. This includes understanding what happens when your IP gets blocklisted.
• Monitoring for anomalies: Implement advanced monitoring to detect sudden spikes in bounce rates or blocklist listings that might indicate a widespread issue beyond individual sending practices.

Key findings

• Routine process anomaly: Barracuda's official (though brief) response suggested the issue stemmed from a "routine transient spike in blacklisted IPs as part of the threat analysis process" that escalated beyond normal parameters.
• Older blocks reactivated: Internal communications from Barracuda support implied that "older blocks" of IPs might have been inadvertently reactivated or flagged, leading to the false positives.
• Lack of detailed explanation: The public documentation and statements provided minimal technical detail regarding the exact mechanism of failure or the specific criteria that led to the widespread listings.
• Focus on threat analysis: Barracuda's emphasis on "threat analysis process" highlights their use of automated systems to identify and block potential sources of malicious or unwanted email, even if these systems can err.

Key considerations

• Automation risks: This incident serves as a case study for the risks associated with overly aggressive or flawed automation in email security, where legitimate traffic can be caught in wide-net blocks.
• Importance of clear policy: For email senders, understanding major blocklist operators' published policies (even if outdated, like the `emailreg.org` reference) provides context for delisting efforts, although direct contact may be more effective during outages.
• IP abuse trends: Broad IP blocklisting, even if erroneous, points to the broader context of IP abuse on the internet. Research from RIPE Labs indicates that spam, malware, and DDoS attacks are major forms of IP abuse, influencing blocklist behaviors.
• Adaptation to threat landscapes: Security vendors like Barracuda continuously adapt their defenses to new threats. For instance, recent reports from Palo Alto Networks highlight critical vulnerabilities found in Barracuda's own products, showcasing the constant evolution of cyber security challenges.