Besides Spamhaus, what blocklists are important for email marketers to monitor?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 May 2025
Updated 16 Aug 2025
5 min read
When discussing email deliverability and sender reputation, Spamhaus often comes up as the most impactful blocklist (or blacklist). And for good reason, its listings can severely hamper your email campaigns. However, focusing solely on Spamhaus can leave you vulnerable to other reputation issues that quietly undermine your inbox placement.
While Spamhaus is undeniably critical, a comprehensive deliverability strategy requires monitoring a broader array of email blocklists. These additional lists, sometimes acting as canaries in the coal mine, provide early warnings about deteriorating sender reputation or problematic list hygiene practices. Ignoring them can lead to subtle yet significant drops in email performance.
Understanding the various types of blocklists is the first step toward effective monitoring. While all blocklists aim to reduce spam, they do so through different methodologies, targeting specific types of abusive behavior. This means a listing on one blocklist doesn't necessarily imply a listing on another, or for the same reason.
Most blocklists can be broadly categorized as IP-based or domain-based. IP-based blocklists, like many of Spamhaus's lists, focus on the sending IP address associated with suspicious email activity. Domain-based blacklists, conversely, target the domains or URLs found within the email content itself. Both are crucial for maintaining a clean sending reputation.
The relevance of a blocklist often depends on how widely it is consulted by internet service providers (ISPs) and mailbox providers (MBPs). While some lists are highly influential across the board, others might only affect deliverability to a specific subset of recipients. This variance underscores the need for diverse monitoring.
Many email providers utilize multiple DNS-based blocklists (DNSBLs) to filter incoming mail. A listing on any of these can lead to messages being rejected, sent to spam folders, or delayed, directly impacting your email marketing performance. It's a complex ecosystem that requires continuous vigilance.
Important blocklists and their impact
Beyond Spamhaus, several other blocklists warrant attention from email marketers due to their specific triggers and potential impact on deliverability. Monitoring these can give you a more complete picture of your sender reputation and help you address issues before they escalate.
SpamCop is widely known for aggregating user complaints. If your IP or domain appears on SpamCop's blacklist, it's a strong indicator that your subscribers are marking your emails as spam. This list can have a noticeable effect on deliverability, even if it's considered less impactful than Spamhaus by some.
SORBS (Spam and Open-Relay Blocking System) primarily lists IP addresses that have sent mail to spam traps or are associated with open relays. A SORBS listing is a clear signal of poor data collection or list hygiene practices. It often means your emails are reaching unengaged or invalid addresses, which can severely damage your sender reputation over time.
Invaluement (IVM) is a collection of blocklists that specifically target senders who have issues with contact acquisition. If you find yourself on an Invaluement blacklist, it's a strong indication that your list-building methods or validation processes need immediate attention. This is particularly relevant for marketers who prioritize list quality.
Blocklist
Type
Primary Focus
Impact
SpamCop
IP-based
User spam reports
Early warning for high complaint rates, can affect deliverability
SORBS
IP-based
Spam traps, open relays, compromised servers
Indicates poor list hygiene or compromised systems
Invaluement
IP/Domain-based
Poor contact acquisition methods
Highlights issues with list building and consent
URIBL / SURBL
Domain/URL-based
Domains and URLs found in spam messages
Can impact click-through and content filtering, regardless of IP status
Each of these blocklists, or blacklists, offers a unique perspective on your sending behavior. A listing on any of them should prompt an investigation into your email practices.
Proactive monitoring and mitigation
The real benefit of monitoring a variety of blocklists extends beyond simply identifying a problem. It's about getting ahead of potential deliverability issues. Many minor blocklist listings act as early indicators, signaling that your email practices might be drifting into risky territory before major mailbox providers take notice.
Proactive monitoring allows you to identify which email blacklists are most important for your specific sending patterns and target audience. For instance, if you primarily send to B2B audiences, some niche blocklists might carry more weight than for B2C senders. Tailoring your monitoring efforts can save you time and prevent unnecessary panic.
When a listing occurs, understanding the specific blocklist's criteria is essential for effective delisting. Each blocklist has its own procedures, and a one-size-fits-all approach to removal is rarely successful. This often involves reviewing recent sending activity and improving list quality. Knowing what to do if listed is as important as the monitoring itself.
Ultimately, the goal isn't just to get off a blacklist, but to stay off. This involves consistently maintaining rigorous list hygiene, implementing proper email authentication (like SPF, DKIM, and DMARC), and ensuring your content is relevant and welcomed by recipients.
Key steps for healthy email sending
Maintain list hygiene: Regularly clean your subscriber lists to remove inactive or invalid addresses. This significantly reduces bounce rates and spam trap hits.
Implement authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned for all sending domains.
Monitor engagement: Pay attention to open rates, click-through rates, and complaint rates as indicators of list health.
Avoid spam traps: Never send to purchased or old lists that might contain spam trap addresses.
Respect unsubscribes: Process all unsubscribe requests promptly and automatically to prevent complaints.
Views from the trenches
Best practices
Actively monitor all dedicated IPs for any listings on various blocklists.
Maintain open communication with customers to understand their sending practices.
Prioritize list hygiene to prevent spam trap hits and reduce complaint rates.
Common pitfalls
Failing to understand the specific triggers for a SORBS listing and other blocklists.
Dismissing listings on less prominent blocklists as insignificant or irrelevant.
Not having a clear action plan for delisting from various blacklists.
Expert tips
View minor blocklist listings as early warning signals or 'canaries in the coal mine.'
Understand that different blocklists affect deliverability to different extents.
Be particularly concerned about Spamcop listings, as they indicate high complaint rates.
Marketer view
Marketer from Email Geeks says Spamhaus is the primary blocklist to monitor, others might be secondary indicators that something else is about to happen.
2021-06-28 - Email Geeks
Expert view
Expert from Email Geeks says Spamcop can significantly affect delivery and serves as an early warning for potential issues.
2021-06-28 - Email Geeks
Securing your email future
Effective email marketing hinges on strong deliverability, which is directly tied to your sender reputation. While Spamhaus remains a cornerstone of the email anti-spam landscape, a holistic approach to blocklist (blacklist) monitoring is indispensable for maintaining consistent inbox placement across various mailbox providers.
By understanding the roles of different blocklists like SpamCop, SORBS, and Invaluement, and proactively managing your sending practices, you can safeguard your email program, avoid costly disruptions, and ensure your messages consistently reach their intended audience. Comprehensive monitoring is a proactive step toward long-term email marketing success.
Spamhaus
0Spam
Cisco
NoSolicitado
URIBL
abuse.ro
ALPHANET
Anonmails
Ascams
BLOCKEDSERVERS
Calivent Networks
EFnet
JustSpam
Kempt.net
NordSpam
RV-SOFT Technology
Scientific Spam
Spamikaze
SpamRATS
SPFBL
Suomispam
System 5 Hosting
Team Cymru
Validity
www.blocklist.de Fail2Ban-Reporting Service
ZapBL
2stepback.dk
Fayntic Services
ORB UK
technoirc.org
TechTheft
SpamCop
SORBS
Invaluement
