What are examples of insignificant or ineffective email blocklists?

Key findings

• Variable impact: The relevance of any real-time blocklist (RBL) or DNS-based blocklist (DNSBL) is directly proportional to whether the recipient's mail transfer agent (MTA) actually uses it. A blocklist might be insignificant globally, but critical if a key recipient uses it.
• Pay-to-delist schemes: Some blocklists operate on a model that allows senders to pay for removal. This practice often nullifies the integrity and spirit of a blocklist, making them less credible in the eyes of reputable ISPs and deliverability experts.
• Niche or hobbyist lists: There are many blocklists that are maintained by individuals or small groups, often with limited reach or specific, sometimes eccentric, listing criteria. These are generally not impactful for broader email deliverability. For more on this, see common issues with hobbyist email blocklists.
• Informational services: Some DNSBLs are not designed to block email but rather to provide informational context, such as identifying newly registered domains or country-specific IP ranges. While useful for analysis, they don't directly block mail.

Key considerations

• Context is king: A listing on an obscure blocklist becomes significant only if one of your intended recipients uses that specific blocklist for filtering. This highlights the importance of understanding your audience's mail infrastructure.
• Prioritize monitoring: Focus your blocklist monitoring efforts on the most impactful and widely used blocklists, such as Spamhaus and Proofpoint. For guidance, consider which email blacklists are most important to monitor.
• Avoid overreacting: Do not panic over every listing from obscure blocklist checkers that query hundreds of irrelevant lists. Investigate actual delivery issues and consult the recipient's bounce messages to pinpoint the blocking source.
• Understanding impact: Assess the actual impact of a blocklist listing on your email deliverability. Mailgun's guide on how to get removed from a blocklist emphasizes this distinction.

Key opinions

• Skeptical view of niche lists: Many marketers consider blocklists like SORBS and UCEProtect to be particularly problematic due to their listing practices or business models, especially when they offer 'pay-to-delist' options.
• Revenge listings: There is a known risk of maintainers of less reputable blocklists engaging in 'revenge listings' if their methods or efficacy are publicly questioned, posing a risk to senders.
• Contextual importance: A blocklist's significance is often tied to whether a specific recipient's mail server uses it. Even an obscure list can become highly relevant if it impacts delivery to a key contact.
• Over-alerting: Some blocklist checking tools that query hundreds of DNSBLs can cause unnecessary alarm among customers. Marketers report frequently having to explain that a listing on an obscure list has no real impact.

Key considerations

• Focus on major blocklists: Prioritize monitoring for the most important email blacklists that are widely used by major ISPs, such as Spamhaus and Barracuda. Ignoring these can significantly impact deliverability.
• Understand listing criteria: Be aware of the listing criteria for different blocklists. Some, like UCEProtect, use aggressive aggregation policies that can lead to wide-ranging, seemingly unjustified listings.
• Evaluate impact before action: Before investing time and effort into delisting, verify if a particular blocklist genuinely affects your email deliverability. Not all listings are created equal. This aligns with advice on what an email blacklist is.
• Consider alternatives: If a blocklist is known for pay-to-delist or arbitrary listings, it's often more effective to monitor your actual inbox placement rates with key recipients rather than engaging with the blocklist itself. For more, see how important SPAMCOP and SORBS are.

Key opinions

• Impact is recipient-dependent: An expert from Email Geeks states that all blocklists are insignificant until one that lists you is used by a recipient you're trying to mail, at which point it becomes the most significant list for that specific interaction.
• Problems with over-checking: Experts express frustration with testing sites that check 200+ DNSBLs, as customers often panic about listings on irrelevant lists, demanding delisting without evidence of actual delivery impact.
• Categorizing blocklists: A former deliverability expert from Email Geeks describes categorizing DNSBLs based on urgency: 'Get everyone out of bed, NOW', 'Who cares?', and 'No point alerting, because you will never get unlisted'.
• Niche examples: RFC-Ignorant is cited as an example of a list that might block senders from Google Workspaces, and other examples include 'Spam Eating Monkey' (SEMFRESH) for informational purposes, and 'lucky7' (blocks IPs with a 7).

Key considerations

• Strategic alerting: Develop a clear strategy for which blocklist alerts warrant immediate action and which can be disregarded, based on their known impact on your critical email flows. This requires a deep understanding of blocklist relevance.
• Avoid unnecessary delisting efforts: Do not waste time and resources trying to get removed from blocklists that have no practical effect on your deliverability, especially those with unreasonable delisting policies or a history of retaliation. Understanding RFC-Clueless blocklist listings is important here.
• Consult trusted resources: Leverage expert opinions and industry resources to distinguish between truly important blocklists and those that are insignificant. This helps in building a robust deliverability strategy.
• Proactive reputation management: Instead of reacting to every blocklist, maintain a strong sender reputation through good sending practices. This minimizes the chance of landing on any blocklist, relevant or not. A guide to email blacklists 101 can offer further insight.

Key findings

• RFC 6471 guidance: RFC 6471 provides an overview of best email DNSBL operational practices, guiding how reputable blocklists should function and how they should be used by mail servers. It helps define what constitutes a 'good' blocklist.
• Purpose of DNSBLs: Documentation emphasizes that DNSBLs are primarily designed to help reduce unsolicited bulk email (UBE), or spam. Their effectiveness hinges on accurate and timely data about malicious sending IPs and domains.
• Distinction in types: Documentation implicitly (and sometimes explicitly) distinguishes between blocklists that are broadly adopted and those that serve highly specific or private purposes, or are purely informational.
• Ethical considerations: While not always prescriptive, the spirit of RFCs and community best practices discourages practices like 'pay-to-delist' or retaliatory listings, as they undermine the anti-spam mission.

Key considerations

• Adherence to standards: Senders should favor engaging with blocklists that clearly adhere to documented operational best practices, as outlined in RFCs. This ensures a more predictable and fair process for delisting.
• Transparency in listing: Reputable blocklists provide clear reasons for listings and transparent delisting procedures. Blocklists lacking this transparency may be considered less significant by many email systems. More information can be found in this in-depth guide to email blocklists.
• Focus on actionable data: Prioritize data from blocklists that provide actionable insights and are demonstrably used by the ISPs or recipient domains that matter most to your email program. For example, RFC 6471 section 2 offers guidance on DNSBL usage.
• Continuous learning: Stay updated with RFCs and industry best practices. This knowledge empowers senders to critically evaluate new or obscure blocklists and avoid unnecessary troubleshooting. Learning what an email blacklist is is a good starting point.