What caused the widespread Barracuda IP blacklist issues in June 2019?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 May 2025
Updated 19 Aug 2025
8 min read
The email landscape in June 2019 saw a significant disruption, particularly for senders relying on various email service providers. A widespread IP blacklist event occurred on the Barracuda Reputation System, leading to considerable challenges for legitimate email senders. Many suddenly found their email deliverability severely impacted, with messages being blocked or routed to spam folders, despite having clean sending practices.
This incident highlighted the critical role that major blocklists (or blacklists) like Barracuda play in email security and the ripple effects when their systems encounter anomalies. Understanding what transpired during this period can offer valuable insights into the dynamics of email blocklists and the importance of vigilant sender reputation management.
In mid-June 2019, numerous email service providers (ESPs) and individual senders began reporting an unprecedented surge in IP addresses listed on the Barracuda Reputation System. This wasn't an isolated issue affecting a single sender or a small set of IPs, but rather a broad phenomenon that caught many in the email deliverability community by surprise. Reports surfaced from various platforms, indicating a systemic problem rather than individual sender misconduct.
Many users, including those with meticulous email hygiene and engagement practices, found their primary sending IPs blacklisted. The suddenness and scale of the listings raised immediate concerns and confusion, as affected senders struggled to identify the root cause of their unexpected poor sender reputation. It became clear that something unusual was happening upstream at Barracuda.
Initially, the exact cause remained unclear, with some speculating about links to other blacklists like MSRBL, though Barracuda typically doesn't use MSRBL by default. The sheer volume of new listings suggested a technical anomaly within Barracuda's system rather than a sudden, global surge in spam from reputable senders. This created a frantic scramble for information and a solution among affected organizations.
The situation was broadly discussed within the industry, with many deliverability professionals noting the significant uptick in Barracuda IP blocks. An article from Word to the Wise provided early insights into the unfolding situation, confirming the widespread nature of the problem and the general confusion among email professionals.
Impact and confusion
The immediate impact of these widespread listings was severe for businesses and organizations whose email communications were suddenly halted or severely delayed. Transactional emails, marketing campaigns, and critical business communications were all affected, leading to potential revenue loss and communication breakdowns. The lack of clear communication or immediate resolution from Barracuda exacerbated the frustration.
Many affected senders reported submitting delisting requests through Barracuda's portal, only to find the process unresponsive or slow. Some even noted that the removal request form wasn't sending auto-responses as it normally would, suggesting an overload or malfunction in their system. The inability to quickly delist their IPs added to the operational difficulties and highlighted a significant gap in their incident response at the time.
The issue was particularly frustrating for senders who maintained strict email sending practices, such as only sending to engaged subscribers and regularly cleaning their lists. Their adherence to best practices made the blocklisting (or blacklisting) seem arbitrary and unjust, adding to the general sense of confusion and helplessness experienced by many in the community. This scenario underscores the importance of understanding how to resolve Barracuda blocklist issues and proactively monitoring your sender reputation.
Some reports indicated that Barracuda's support suggested that the affected IPs were "older blocks" that had been "resurrected" or relisted for reasons unknown to their current logs. This explanation, while offering a possible technical clue, did not fully alleviate the immediate operational distress faced by senders with hundreds of IPs suddenly blocklisted.
Barracuda's response and resolution
Barracuda eventually issued a statement addressing the widespread IP blacklist issues. They attributed the problem to a "routine transient spike in blacklisted IPs as part of the threat analysis process" that normally goes unnoticed. However, in this particular instance, it appears something went awry, leading to an abnormal number of legitimate IPs being caught in the net. This explanation, detailed in a Barracuda update by Laura Atkins, provided some clarity, though many in the community questioned how an "18,000% increase" in listings could be considered routine.
Initial support responses were often generalized or only addressed a small number of IPs. Senders were advised to manually provide extensive lists of affected IP addresses via email. This manual process, while eventually leading to some delistings, was inefficient given the scale of the problem. It showcased the challenges major email security vendors face when their automated systems experience unexpected anomalies.
Barracuda delisting contacttext
intent@barracuda.com
Over the following days, senders started reporting a gradual improvement in their listings, with many seeing a significant drop in blocklisted IPs. While the precise technical glitch was never fully disclosed by Barracuda beyond the initial statement, the situation eventually normalized, indicating that internal adjustments or fixes were deployed to correct the erroneous listings. This incident highlighted the need for transparency and rapid communication from major blocklist operators during widespread outages or misconfigurations.
Key takeaways and preventative measures
The Barracuda IP blacklist event of June 2019 serves as a stark reminder of how critical robust email deliverability strategies are. Even with pristine sending practices, external factors like blocklist anomalies can unexpectedly disrupt email flow. This reinforces the need for senders to have proactive monitoring and quick response plans in place. Understanding what is an email blacklist and how it works is essential for navigating such challenges.
For senders, maintaining excellent sender reputation goes beyond simply avoiding spamming. It involves continuous vigilance, understanding various blocklist mechanisms, and having strategies for rapid mitigation. A key takeaway from this event is that even reputable IPs can be temporarily caught in automated systems' crosshairs, emphasizing that how your email address ends up on a blacklist isn't always straightforward.
Regularly checking your IP and domain status across major blocklists (or blacklists) is a foundational step. Implementing double opt-in processes for new subscribers can help prevent the acquisition of invalid or problematic email addresses that could trigger blocklist activations upon initial sends. Such an incident also underlines the value of having diverse sending infrastructure, where possible, to minimize the single point of failure.
Proactive risk mitigation strategies
Monitor continuously: Regularly check your sending IPs and domains against major public and private blocklists.
Implement double opt-in: Verify subscriber consent to minimize spam traps and invalid addresses.
Maintain list hygiene: Regularly remove inactive or unengaged subscribers to improve sender reputation.
Diversify sending IPs: If sending high volumes, distribute traffic across multiple IPs to reduce impact of a single listing.
This event also brought to light the operational challenges faced by email service providers when dealing with widespread blacklisting events affecting their shared IP pools. Swift internal communication and coordination with the blocklist operator become paramount to minimize disruption for their customers.
Views from the trenches
Best practices
Maintain high engagement rates to build a strong sending reputation that can better withstand anomalies.
Keep detailed records of your IP addresses and sending volume to assist with delisting requests.
Stay informed about major industry incidents and changes in blocklist policies.
Common pitfalls
Assuming clean practices alone guarantee immunity from blocklists, as system anomalies can still occur.
Relying solely on automated delisting tools without understanding underlying issues or manual options.
Neglecting communication with your ESP or blocklist provider during widespread incidents.
Expert tips
Implement robust monitoring for all your sending IPs across various blacklists to detect issues quickly.
Develop a clear internal process for responding to major blocklist events, including who to contact and how.
Prioritize double opt-in for subscriber acquisition to enhance list quality and reduce invalid sign-ups.
Marketer view
Our primary sending IP got listed, even though our email practices are very clean, with active re-engagement journeys and strict rules about sending to engaged subscribers. We suspected it might have been caused by someone using a bad address during our online rewards program sign-up.
June 17, 2019 - Email Geeks
Expert view
There was an increase in listing activity late last week and early this week, and Barracuda doesn't use MSRBL by default, so it's likely an internal Barracuda issue.
June 17, 2019 - Email Geeks
Conclusion: Learning from the Barracuda incident
The widespread Barracuda IP blacklist issues of June 2019 served as a critical learning experience for the email industry. It underscored that even sophisticated blocklist systems can encounter internal anomalies that lead to significant, albeit temporary, disruptions for legitimate senders. While Barracuda eventually resolved the problem, the incident highlighted the importance of robust communication channels and efficient delisting processes during such events.
For senders, the episode reinforced the perennial message: maintain impeccable email hygiene, prioritize engaged subscribers, and invest in vigilant monitoring of your email deliverability metrics. Being proactive in managing your sender reputation is the best defense against unforeseen external events, ensuring your messages continue to reach their intended inboxes.
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