Are there good alternatives to MXToolbox for blocklist API aggregation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 21 Jun 2025
Updated 19 Aug 2025
7 min read
Managing email deliverability is a multifaceted challenge, and staying off blacklists (or blocklists) is a critical component of that effort. Many of us rely on aggregation services to check our IP addresses and domains against numerous real-time blocklists (RBLs) and DNS blacklists (DNSBLs) without having to query each one individually. MXToolbox has long been a go-to for this, offering a comprehensive check of various blocklists in one place.
While useful, some users seek alternatives, often looking for more reliable API access, specific feature sets, or simply a different user experience. I've encountered the frustration of trying to sign up directly with major blocklist providers, even Spamhaus, finding the processes cumbersome despite their crucial role in email security. The desire for a centralized, easy-to-use API for blocklist monitoring is definitely shared across the industry.
The core issue is that while many individual blocklist services exist, aggregating their data reliably and programmatically through an API can be surprisingly difficult. It is a pain to manually check each blocklist, and many of the bigger ones might block mass DNS queries if you try to build your own system from scratch. This is where dedicated aggregation tools become invaluable.
For many, the appeal of a service like MXToolbox lies in its aggregation of multiple blocklist checks into a single query. This saves significant time and effort compared to manually querying each list. However, relying on a single tool for such critical data can have drawbacks, including potential rate limits, specific list coverage, or integration challenges with existing systems.
The main challenge with direct blocklist integration is the sheer number of lists and their varied access methods. Some require paid subscriptions, others might necessitate downloading and installing specific software, while still others have complex API documentation or strict usage policies. This fragmented landscape makes a consolidated approach very appealing for email service providers (ESPs) and large senders.
Building your own blocklist monitoring service from scratch is a significant undertaking. While technically feasible, it requires substantial development resources to manage API integrations, handle parsing of different data formats, implement caching, and maintain consistent uptime. The effort often outweighs the benefits for most organizations, pushing them towards existing solutions.
The complexity of direct integration
Integrating directly with individual blacklists (or blocklists) means navigating diverse API structures, authentication methods, and response formats. This requires significant developer resources to build and maintain robust connections, making it a less feasible option for many.
API limitations: Many blocklists are not designed for high-volume programmatic queries without prior arrangements.
Cost: Subscribing to multiple premium blocklists can quickly add up, often exceeding the cost of an aggregator.
Maintenance: Each blocklist's system can change, requiring ongoing updates to your integration.
Other blocklist API aggregators
Many tools offer blocklist checking, some with more robust API capabilities than others. HetrixTools is one often mentioned, though I've heard mixed feedback regarding its reliability for large-scale queries and whether it's still actively maintained by a substantial team. While its web lookup tool is visually appealing, API stability for mass checks is crucial for any serious user.
RBLTracker is another strong contender that frequently comes up in conversations. Users generally praise its responsiveness, especially in adding new RBLs (real-time blacklist) like those from Abusix. Its ability to quickly adapt to the evolving blocklist landscape makes it a valuable asset for comprehensive monitoring. For those managing multiple clients or extensive IP ranges, such features are incredibly important.
Emaildojo.io also had a free checker that would notify you of listings, though its current maintenance status is uncertain. Beyond these, services like Postmastery and InboxMonster are frequently used by professionals, each offering different levels of insight and focus, some even exploring blocklist monitoring as an add-on to broader deliverability services. EasyDMARC and Mailmonitor are examples of tools that are beginning to offer this functionality alongside their primary DMARC reporting or email monitoring services.
Mixed feedback on scalability for very large-scale queries.
RBLTracker
Comprehensive blocklist coverage, timely updates, good support for adding new RBLs.
Generally positive, considered robust for ongoing monitoring.
Emaildojo.io
Limited free checker, email notifications for listings.
Uncertain status regarding ongoing maintenance and API availability.
What to look for in an alternative
When evaluating an alternative to MXToolbox for blocklist API aggregation, several factors should weigh heavily in your decision. Beyond just the number of blocklists checked, consider the accuracy and timeliness of the data. Delays in reporting a new listing, or false positives, can significantly impact email campaigns.
API reliability and ease of integration are also paramount, especially for larger organizations or ESPs. A well-documented API, consistent uptime, and clear usage limits prevent operational headaches down the line. Look for services that offer detailed reporting beyond just a 'listed/not listed' status, providing context on the specific blocklist and potential reasons for the listing.
Finally, consider the level of support provided. For critical issues like an unexpected listing, responsive and knowledgeable support can make all the difference in quickly resolving the problem and mitigating impact on your email deliverability. While cost is always a factor, prioritizing a robust and reliable service over the cheapest option will likely save you more in the long run by preventing deliverability outages.
What to look for
Comprehensive Coverage: Ensure it checks all major and relevant blocklists (e.g., Spamhaus, Proofpoint, etc.).
Real-time accuracy: Timely updates are crucial for proactive mitigation.
API robustness: A stable, well-documented API with sufficient rate limits.
Alerting features: Customizable notifications for new listings or delistings.
Detailed reporting: Insights into the listing reason and delisting process.
Common pitfalls
Outdated data: Some free or less maintained tools may not reflect current blocklist statuses.
Limited list inclusion: Only checking a few blocklists might miss critical listings.
Poor API documentation: Makes integration difficult and prone to errors.
Lack of support: Critical if you face delisting challenges or need technical assistance.
Cost over value: Opting for the cheapest option might result in unreliable data or missing features.
Integrating blocklist data into your deliverability strategy
Blocklist monitoring is a reactive measure, informing you when something has already gone wrong. A holistic approach to email deliverability also involves proactive strategies to maintain a healthy sender reputation and avoid listings in the first place. This includes proper email authentication (SPF, DKIM, DMARC), managing bounce rates, and ensuring clean recipient lists.
Many tools that offer blocklist monitoring are part of broader email deliverability suites that provide insights into inbox placement, spam trap hits, and authentication issues. Integrating blocklist checks into a larger monitoring strategy allows for a more complete picture of your email program's health. For example, understanding how a specific blocklist impacts your delivery to Gmail or Yahoo Mail can inform your remediation efforts.
While blocklist APIs are essential, consider them a data source within a larger deliverability intelligence system. Your own internal systems or a dedicated deliverability platform can aggregate this data, along with DMARC reports, ISP feedback loops, and inbox placement tests, to provide a single pane of glass for monitoring and managing your sender reputation. This integrated approach ultimately leads to better inbox placement and email program performance.
Example DNS query for a Spamhaus Zen listingBASH
dig +short -t A 1.0.0.127.zen.spamhaus.org
127.0.0.2
Views from the trenches
Best practices
Actively monitor your IPs and domains across multiple reputable blocklists (e.g., Spamhaus, Proofpoint, etc.).
Automate blocklist checks using an API aggregator for efficiency and timely alerts.
Prioritize actionable insights; understand *why* you were listed to address root causes.
Maintain clean email lists and adhere to best sending practices to proactively avoid future listings.
Common pitfalls
Relying solely on one blocklist checker or free tools that may not provide comprehensive or up-to-date data.
Ignoring less prominent blacklists, as even minor listings can impact deliverability at some ISPs.
Delaying delisting requests; quick action is essential to minimize sending disruptions.
Not understanding the root cause of a listing, leading to repeated blocklistings.
Expert tips
Set up automated alerts for any new blocklist listings so you can respond immediately.
Regularly review your email sending practices to prevent issues that lead to blocklistings.
Understand the differences between various blocklists; some are more impactful than others.
Consider a comprehensive deliverability platform that combines blocklist monitoring with other metrics.
Marketer view
Marketer from Email Geeks says they resorted to MXToolbox's paid service after struggling with the sign-up processes and API access for individual blocklist providers, finding it hard to support smaller, independent projects despite wanting to.
2024-08-04 - Email Geeks
Marketer view
Marketer from Email Geeks says they found HetrixTools to have a nice web lookup tool, but were unsure about its reliability for checking thousands of IPs at once, suggesting it might be a smaller, less scalable project.
2024-08-05 - Email Geeks
Final thoughts on blocklist aggregation
Finding the right blocklist API aggregator can significantly streamline your email deliverability efforts. While MXToolbox offers a widely recognized service, several robust alternatives provide comprehensive coverage, reliable APIs, and actionable insights. Services like RBLTracker stand out for their responsiveness and thoroughness, addressing the core need for aggregated, up-to-date blocklist information.
The key is to prioritize accuracy, timeliness, and ease of integration when selecting a tool. Remember that blocklist monitoring is a critical component of a broader deliverability strategy that includes proper authentication, list hygiene, and proactive reputation management. By choosing the right tools, you can ensure your emails consistently reach the inbox, protecting your sender reputation and maximizing your email program's effectiveness.
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
HetrixTools
RBLTracker
Emaildojo.io
