DNS blocklists – the bouncers at the door of your network, safeguarding your people, data, and systems. Like a VIP list at a club, blocklists provide security solutions with a curated database of known “bad actors” to automatically deny access.

Malicious IPs try to spam your inboxes? Denied. Phishing site attempts to steal your creds? Access revoked. The latest malware outbreak comes knocking? Do not pass go, do not collect $200.

But what goes on behind the scenes to craft these critical threat intelligence tools? What options exist for implementing blocklist defenses? How do you avoid being unfairly “blocklisted” yourself?

This comprehensive guide explores everything DNS blocklists, from core concepts to configuration best practices and the future of DNS-based security. Read on to learn how blocklists function, top sources to leverage, and tips for successful layered blocking at scale.

Time to roll out the virtual red carpet for your organization’s legitimate traffic, and leave the cyber riff-raff waiting outside.

Page Contents

What are DNS Blocklists and How Do They Work?

DNS blocklists, sometimes referred to as blacklists or blocklists, are databases ofIP addresses, domains, and other internet resources that are known to beassociated with malicious cyber threats or high-risk behavior. By checking incoming network connections and communications against these blocklists, organizations can proactively block threats like spam, malware, phishing scams, and more. But what exactly are DNS blocklists and how do they function to keep networks secure? Let’s explore the basics.

Defining DNS Blocklists

DNS blocklists contain lists of internet resources that have been flagged as malicious or untrustworthy. Some key things to know:

  • They come in a few main flavors – IP-based blocklists, domain-based blocklists, and hash-based blocklists. More on this later.
  • Blocklists can operate in real-time or use historical DNS data. Again, more later.
  • They are maintained by specialized security companies and groups who research and catalog threats.
  • Blocklists don’t actually block anything themselves – they just provide data that network security tools use to block threats.

So in summary, a DNS blocklist is a database that provides IP addresses, domain names, hashes, or other identifiers of known threats. This allows security solutions to cross-reference connections against these lists and stop cyberattacks before they occur.

How DNS Blocklists Function

DNS blocklists function by allowing security tools to instantly check connections against a database of known bad actors. Let’s look at an example:

  1. An email from [email protected] comes in to your network mail server.
  2. Your email security platform checks the domain against DNS blocklists.
  3. is found in a domain-based blocklist of known phishing sites.
  4. The email security platform automatically blocks the email, keeping your users safe.

This entire process typically happens in milliseconds, providing near real-time protection against threats. And it can happen at different stages, like checking the sender’s IP reputation, the domain reputation, and even the content hash. Blocklists supercharge security.

IP-based vs Domain-based vs Hash-based Blocklists

Not all DNS blocklists are created equal. The three main types are:

IP-based blocklists – These contain lists of IP addresses known to be associated with threats like spam, malware, botnets, and more. An example is Spamhaus’s famous Spamhaus Block List (SBL).

Domain-based blocklists – These blocklists contain domain names that are known to be risky or malicious, often based on historical usage patterns. The Spamhaus Domain Blocklist (DBL) is a good example.

Hash-based blocklists – These blocklists use cryptographic hashes of spam email content, malware files, and other threats to identify bad traffic without needing the full URL, IP, or domain.

Each type has its own strengths and uses. For example, IP lists are great for blocking senders early at connection time, while hash-based lists allow blocking malicious content without needing all the context. Layered together, they offer comprehensive protection.

Real-time vs DNS-based Blocklists

In addition to different content types, DNS blocklists also come in two main flavors when it comes to their operation:

Real-time blocklists – As the name suggests, these blocklists operate in real-time by directly observing current traffic and requests. As soon as a threat is detected, it is added to the blocklist. These offer instant protection.

DNS-based blocklists – These blocklists rely on historical DNS data along with threat research to build a database of known bad domains, IPs, and other indicators. They may not be quite as fast acting as real-time lists, but provide breadth.

In summary, DNS blocklists are curated databases of different types of cyberthreat indicators that security tools rely on to filter out traffic from risky sources,stop malware, and block other attacks. They act as a first line of automated defense in depth for modern networks and users. By understanding the basics of how they work, organizations can more effectively leverage them as part of a robust security strategy.

Why are DNS Blocklists Important for Security?

DNS blocklists may seem simple in concept, but they provide a profoundly important layer of protection against cyber threats. By leveraging curated databases of known threats, blocklists allow organizations to automatically filter out huge amounts of dangerous traffic that could compromise security. Let’s explore some of the key benefits DNS blocklists offer if implemented properly.

Blocking Spam and Malicious Email

One of the most common and impactful uses of DNS blocklists is to block unwanted email spam and more malicious phishing emails.

Nobody likes having their inbox clogged with useless spam for knockoff pharmaceuticals or fake Nigerian princes. By maintaining IP and domain blocklists of known spam senders, email systems can automatically reject up to 90% of unwanted spam messages before they ever reach your employees. This significantly reduces annoyance and saves security teams time.

More critically, quality blocklists also provide real-time protection against phishing emails – one of the top cyber attack vectors. Checking incoming emails against hashed blocklists of known phishing content allows security tools to block clever social engineering emails that impersonate trusted brands. This prevents employees from being tricked into clicking malicious links or attachments that could compromise systems.

Preventing Malware Infections

Email isn’t the only vector blocklists help protect. DNS blocklists are an essential tool for preventing malware infections from compromised sites or downloads.

By maintaining updated lists of domains and IP addresses known to be hosting malware or command and control servers, organizations can use DNS filtering and proxies to block access attempts.

For example, a user clicks a link in an email which leads to a site controlled by cyber criminals. That site hosts malware payloads designed to download onto the user’s device when they visit. However, because the site domain is listed in a DNS blocklist, the request is automatically rejected at the DNS level, preventing the malware from ever reaching the user’s machine.

This kind of proactive blocking is a key reason cybersecurity experts recommend implementing DNS-based blocking tools to prevent infections. Blocklists stop threats before they land, reducing the need for costly remediation.

Stopping Phishing Attacks

Phishing isn’t limited just to email. Many phishing scams rely on creating fake websites impersonating banks, online services, and other popular destinations.

By maintaining domain-based blocklists of sites flagged for phishing and leveraging DNS filtering, organizations can instantly block access attempts to these malicious sites. Users will get blocked before ever reaching the phishing site, keeping their logins and sensitive info safe.

This offers an important additional layer beyond email security, covering phishing efforts through malvertising, social media, search engines, and other attack vectors that start with clicking a risky link. DNS blocklists prevent successful phishing attacks through blocking at the source.

Restricting Access to Harmful Websites

Beyond purely malicious sites, DNS blocklists also empower organizations to control access to other harmful or unproductive website categories like gambling, drugs, pornography, gaming, social media, and more.

By implementing blocklists focused on these categories and connecting them to local DNS services, groups like schools and businesses can filter certain sites right at the network level based on their acceptable use policies. This saves security teams time babysitting access.

Blocklisting known gambling and drug domains prevents legal liability and remote code execution risks, while blocking access to porn, gaming, and social sites allows organizations to control productivity and network use as they see fit. The use cases are diverse, but the underlying blocklist strategy is the same.

Keeping Ad Tracking in Check

One last area where DNS blocklists provide value is reducing ad tracking and surveillance. Many blocklists maintain updated lists of ad networks, tracking services, and data brokers who monitor user activity across sites for profiling.

By implementing these blocklists at the DNS level or in browser extensions, individuals can significantly reduce how much of their web browsing is tracked and sold by third parties. This improves privacy while reducing annoyances like retargeted ads following you around the internet.

DNS blocking allows filtering out these creepy trackers without breaking websites overall. And browsers like Firefox even maintain their own blocklists of trackers updated automatically. The internet feels a bit cleaner with this kind of filtering in place.

The key takeaway is that well-maintained DNS blocklists provide a powerful weapon in defending against email threats, malware, phishing, inappropriate content, and privacy invasion. By proactively blocking based on constantly updated threat intelligence, organizations can lighten security workloads while automatically stopping a large percentage of attacks before they ever reach end users and systems. DNS blocking is one security layer that most networks simply can’t afford to ignore.

How are Effective DNS Blocklists Created?

DNS blocklists only function properly if the underlying data is accurate, extensive, and up-to-date. But compiling robust DNS blocklists is much more complex than just throwing together some suspicious looking domains. It requires a disciplined, multi-step process. Let’s take a look under the hood at how top-tier DNS blocklists are actually crafted.

Gathering Threat Data from Diverse Sources

The raw material for great blocklists is quality threat data, from as many diverse sources as possible. The top blocklist vendors aggregate data from multiple streams:

  • ISP and Hosting Company Data – Major network providers share insights on spammers and malware they observe across their infrastructure.
  • Honeypots and Dark Web Monitoring – Blocklist companies operate spam traps, honeypots, and monitor dark web sites to detect threats in action.
  • Public Threat Intelligence – Government agencies like CISA provide some public threat intel that feeds blocklists.
  • Security Research Groups – Anti-phishing and abuse fighting groups share research on new scams and threat tactics.
  • End Customers – Blocklist vendors allow customers to submit new threats they encounter for inclusion.

By blending data from their own monitoring with industry submissions and public intelligence, blocklist creators can amass comprehensive threat datasets.

In-Depth Analysis and Policy Definition by Experts

Of course, raw threat data only gets you so far. All that intel must be carefully analyzed by trained security experts before entering any blocklist.

Researchers manually review odd traffic patterns, new domains associated with campaigns, hosting behaviors, and other signals. This allows them to connect the dots and identify true threats.

Blocklist vendors also establish strict policies for what meets the criteria for being included. For example, Spamhaus performs extensive analysis to ensure any IP addresses added to the Spamhaus Block List (SBL) meet their published standards for lacking appropriate spam controls.

Policy definition prevents inaccurate listings while ensuring the blocklists stay focused on only clearcut threats. This meticulous analysis and curation is essential to creating precision security tools.

Regular Updates to Maintain Accuracy

Cyber threats evolve rapidly, so DNS blocklists must be updated extremely frequently to provide current protections.

Top vendors like Spamhaus update their blocklists multiple times per day as new threats are identified and analyzed based on the latest intel. Some list updates happen in as close to real-time as possible.

Regular updates ensure any expired domains or false positives get removed promptly while newly observed threats can be blocked before doing major damage. Out-of-date blocklists lose their value quickly.

For optimal results, organizations should configure their DNS tools to automatically pull list updates on the same accelerated schedule the vendors maintain. This keeps accuracy high.

Large Datasets for Comprehensive Coverage

Size and diversity of datasets also matter when it comes to DNS blocklists’ effectiveness. Lists with limited scope or scale fail to identify many live threats.

Major blocklist compilers like Spamhaus, with over 20 years of experience, have amassed vast databases of known IP and domain threats numbering in the millions to tens of millions of entries.

These large corpuses derived from varied global intelligence sources provide comprehensive visibility into the threat landscape. Smaller blocklists may miss threats simply due to limited inputs.

The bottom line is crafting high-fidelity DNS blocklists requires blending diverse threat data, in-depth expert analysis, constant updating, and sufficient scale. Follow these best practices when evaluating and implementing security blocklists to maximize your protection. Not all lists are created equal.

DNS Blocklist Sources and Providers

With a basic understanding of how DNS blocklists function and the data required, the next question becomes: Where do you actually get robust, reliable blocklists? Let’s survey some of the top blocklist providers and sources available to help protect your organization.

Overview of Top Blocklist Providers

Many security vendors and research groups compile their own DNS blocklists. However, these core providers publish what are considered the most reputable and widely adopted lists:

  • Spamhaus – Non-profit cyber threat tracker, maintains famous lists like the Spamhaus Block List (SBL)
  • SpamCop – Pioneering anti-spam blocklist service since 1998
  • – Swiss research group focused mainly on botnet/malware threats
  • BitDefender – Antivirus leader provides some free blocklists
  • SpamRats – Volunteer-driven community providing spam/malware lists
  • SORBS – Long running anti-spam blocklist project

This is just a sample, as dozens of providers exist. But the important takeaway is focusing on established, vetted sources versus unknown single-person operations.

Spamhaus Data Query Service (DQS)

As one of the oldest and most trusted blocklist compilers, Spamhaus deserves special attention. Their commercially available Data Query Service (DQS) package brings immense value through blending multiple Spamhaus blocklists covering threats like:

  • Spam emails
  • Phishing
  • Malware
  • Botnet/C&C
  • Proxies
  • Policy violations
  • Recent domain registrations

With over 20 finely tuned lists updated in near real-time, anchored by the famous Spamhaus Block List (SBL), the DQS offers one-stop access to irreplaceable threat data. This makes it a go-to recommendation for implementing DNS protection.

Other Leading DNS Blocklist Sources

In addition to Spamhaus, many other reputable blocklist sources exist that may be worth incorporating into a layered security strategy depending on your needs:

  • – Leading nonprofit provider of botnet and malware IOCs
  • BitDefender – Antivirus vendor that offers some free blocklists
  • – Community project offering lists of spam IPs/proxies
  • Bambenek Consulting – Cyber intel company publishing high-value C2 lists
  • SpamRats – Volunteer-based community list focusing on spam IPs
  • squidblacklist – Shared community blacklist of spam and scam domains
  • BrightCloud – Webroot’s domain/IP rep lists covering spam and malware

The key is stacking diverse, reputable sources to maximize your threat coverage.

Choosing Reputable Providers Over Unknown Blocklists

With so many potential sources of blocklist data, it can be tempting to just merge lists from every corner of the internet into one mega-list. However, this can be dangerous.

Many smaller blocklist operators lack the rigorous analysis and policy definition of established vendors. Questionable lists may include inaccurate, outdated, or improperly flagged entries that create false positives blocking legitimate traffic.

Worse, incorporations of some lists are actually privacy violations or illegal depending on jurisdiction. Always vet lists thoroughly and lean on known reliable industry sources. A few solid blocklists from experts beat a haphazard mountain of questionable data.

By partnering with trustworthy providers, implementing their lists in layers, and configuring automatic updates, you can realize the full security potential of DNS blocklists without disruption. They are most effective when leaning on credible, maintained data.

Implementing DNS Blocklists for Maximum Security

Simply having access to robust DNS blocklists is only half the battle. To unleash their full protective power, organizations must properly implement and configure blocklists across different security layers. Done right, this security-in-depth approach can catch a wide spectrum of threats.

Integration Points in Email Infrastructure

Email security offers a prime opportunity to leverage multiple types of layered DNS blocklists to filter threats:

  • At connection – Check connecting IP reputation against RBLs like Spamhaus SBL to catch spamming IPs
  • During SMTP transaction – Block malicious domains in SMTP HELO/MAIL FROM fields via DBLs
  • In content – Scan message content and links against hash/domain lists to catch phishing

Integrating DNS blocklists at each phase allows blocking spam, malware, and phishing threats at different points of email delivery for maximum protection.

Layering Blocklists for Defense-in-Depth

Within each integration point, organizations should deploy multiple well-maintained blocklists to cover a wider range of threats.

For example, an effective email security stack would include:

  • Spamhaus SBL, botnet list, and BitDefender spam list at IP connection
  • Spamhaus DBL domain blocklist during SMTP transaction
  • Spamhaus HBL, malware hashlist, and BitDefender phishing list to scan message content

This blend of different vendor lists and different list types provides overlapping threat visibility for more robust blocking. If one list misses a threat, another may catch it.

Policies for Handling Blocklist Matches

Once integrated into security tools, blocklists simply provide data – the vendor must decide how to handle actual blocklist matches.

Common options include:

  • Quarantine – Flag, isolate, and require manual release for emails matching blocklists
  • Rate limit – Slow down delivery for emails associated with blocklisted IPs
  • Redirect – Reroute emails to honeypots for further spam analysis
  • Reject/block – Immediately bounce or close connection for blocklist matches

Organizations should test different match policies, starting more aggressive. Some “quality score” systems blend lists with internal metrics to fine tune mail handling.

Keeping Blocklists Updated Automatically

To maintain maximum effectiveness over time, organizations must configure security systems to automatically update DNS blocklists on the vendor’s release schedule (often daily or even hourly).

Failing to regularly refresh lists will allow more threats to slip through as new spam campaigns launch or malware adapts. Automated updates ensure you always filter against the latest intelligence.

Some ways to enable automatic blocklist updates:

  • Use DNS vendors who push updates to recursive servers
  • Build scripts to pull new lists from vendors via API or download
  • Deploy security systems with built-in blocklist auto-update features

Keeping lists current should be part of any blocklist integration project. Configure updates during testing phases to avoid protection gaps.

The right blocklists implemented thoughtfully provide powerful, layered threat protection. Take time to carefully integrate diverse lists at multiple points, customize match handling policies, and schedule regular updates. This disciplined approach enables automatic defense against the widest range of cyberattacks.

Getting Off DNS Blocklists (De-listing)

Despite best efforts, sometimes organizations still end up unfairly blocklisted for spam or other policy violations through no fault of their own. Maybe a vendor mistake, or IP space you leased was previously abused before it was assigned to you. When this happens, getting de-listed should become a top priority.

Though frustrating, following the proper de-listing process helps resolve the issue quickly while avoiding further complications down the road. Let’s walk through the steps.

Monitoring Blocklist Status

The first step is knowing you’ve been blocklisted in the first place. Monitor your email traffic and security tools for any unexplained filtering/bouncing of messages that might indicate none of your content is reaching its destination.

You can also proactively check whether your IP addresses or domains appear on major blocklists using tools like Spamhaus’ Blocklist Removal Center. The earlier you detect a problem, the better.

Investigating the Reason for Block-listing

When reaching out to a blocklist vendor or service provider about getting de-listed, it pays to do your homework. Review traffic logs and security reports to determine:

  • Which blocklist(s) have you listed?
  • What was the reason given for the listing? (spamming, malware distribution, etc)
  • Can you identify any events that may have caused the false flagging?

Having these details handy streamlines remediation discussions and demonstrates you’re serious about correcting the issue.

Following Provider Guidelines for Removal Requests

Every major blocklist provider maintains published policies and procedures for requesting removal from their lists.

For example, Spamhaus requires users to specify if they are the IP/domain owner, what listing they are on, and agree to filter policies going forward.

Be sure to read and follow all provider guidelines closely, and provide any required info like API keys or account references. Proper process is required.

Implementing Best Practices to Avoid Future Block-listing

To prevent another round of disruptive blocking once de-listed, implement security best practices like:

  • Carefully monitoring outbound traffic
  • Enforcing stringent email sending policies
  • Updating spam filters and antivirus tools
  • Watching provided IP space closely
  • Limiting exposure of mail servers
  • Fixing any vulnerabilities that could enable spam relays

Following security fundamentals makes repeat listings less likely. And leveraging blocklists yourself helps avoid traffic from compromised networks.

Getting de-listed sometimes requires patience and diligence. But a bit of research, adhering to provider policies, and preventative measures significantly smooth the process. Establish plans for handling false listings before issues arise.

And if problems persist, don’t hesitate to engage a security consultant or email delivery expert for assistance getting back on track. A short-term blocklisting doesn’t have to derail email operations long-term.

Avoiding False Positives with Whitelists

One downside of even the most meticulously maintained DNS blocklists is the potential for false positives blocking legitimate traffic. To counter this, organizations should utilize whitelists or allowlists as exceptions for trusted senders.

Maintaining Allow-lists of Legitimate Senders

Whitelists contain the exact opposite of blocklists – approved domains or IP addresses that should always be allowed, regardless of their reputation.

Common examples to include on email whitelists:

  • Any internal or first-party domains/IPs
  • Business partners
  • Services like payment processors
  • Email vendors
  • Legitimate notifications like bank fraud alerts
  • Emails from staff personal accounts

Building this list of exceptions prevents key traffic from ever being blocked. But keep the list trimmed to only necessary senders to avoid openings for threats.

Exceptions for Internal IPs and Domains

One particularly crucial whitelisting step is adding exceptions for all internal IP ranges and domains used by your organization.

Without proper whitelisting, blocklists could actually block your own inter-office email, websites, and line-of-business tools as their IPs show up on lists.

Closely tracking and whitelisting your public IP space helps avoid this organization-halting mistake. Forgetting internal subnets is a common gotcha.

Regular Review of Whitelists for Optimal Efficiency

To keep whitelists focused only on truly legitimate exceptions, review them regularly for pruning. Just as with blocklists, outdated whitelist entries open unnecessary holes.

Key practices include:

  • Removing decommissioned IPs/domains no longer in use
  • Double checking senders to confirm they still require whitelisting
  • Watching for whitelist rules inadvertently covering broad ranges/patterns
  • Limiting exceptions to the most specific host or address needed
  • Having multiple eyes audit lists to detect unnecessary approvals

Keeping whitelists tight requires work, but pays dividends in avoiding false positives without sacrificing security.

In summary, balanced use of both blocklists and whitelists allows organizations to automate protection against the vast majority of threats while still smoothly delivering business critical email. Define exceptions thoughtfully, implement them carefully, and review them regularly to find the right formula. Precision whitelisting is an art that complements the science of DNS blocklisting.

The Future of DNS Blocklists in Threat Protection

DNS blocklists have proven their worth as a ubiquitous first line of automated defense against cyberthreats. But the threat landscape continues evolving at a rapid pace. To stay effective, both the blocklist data and integration with security stacks must improve. What does the future hold for DNS-based threat blocking?

Leveraging Emerging Technologies Like AI

While today’s top blocklists rely heavily on expert human analysis, machine learning and artificial intelligence are unlocking new horizons for proactive threat data.

By analyzing network traffic patterns at immense scale across millions of data points, AI systems can automatically identify emerging spam campaigns, new malware variant behaviors, and other threats more quickly and precisely than ever before.

Integrating these AI-powered cyber threat models with automated blocklist generation will allow creating and updating lists faster while staying laser focused on the most critical threats. AI augmentation is inevitable.

Responding to New Email Threat Landscape

As email scams grow more sophisticated, blocklists must evolve to detect emerging tactics like:

  • Lookalike domain phishing
  • Logo and branding spoofing
  • Zero-day malware attachments
  • Snowshoe spamming
  • Polymorphic messaging

Fortunately, advances in heuristics and behavioral analytics provide new weapons to identify these tactics based on contextual patterns instead of static signatures. Expect lists to keep getting smarter.

Providing real-time protections beyond email

While email protection dominated early blocklisting use cases, DNS filtering has expanded to secure web traffic, end users, and organizations as a whole.

Real-time, continually updated DNS blocklists allow blocking access to malicious websites, command and control servers, inappropriate content, and more at the network level as users make requests.

This “threat call blocking” model will become essential for timely threat prevention as distributed workforces access cloud apps and services from anywhere. Blocking switches from email to network focus.

The bottom line is that as threats get more advanced, evasive, and distributed, DNS blocklists must get faster, more precise, and integrated into multiple security layers. Organizations that leverage these evolving capabilities will gain significant risk reduction.

Key Takeaways on DNS Blocklists

DNS blocklists offer a powerful first line of automated defense against today’s cybersecurity threats by allowing organizations to proactively block traffic from known malicious sources. Here are the key lessons to keep in mind:

  • DNS blocklists function by providing databases of threat indicators that security tools cross-reference in real-time to stop attacks.
  • Implementing blocklists allows automatically blocking huge amounts of spam, phishing, malware, botnets, and other threats.
  • Blocklists come in different flavors like IP-based, domain-based, and hash-based to provide layered protection.
  • Accuracy and comprehensiveness rely on blending diverse threat data and analysis by experts.
  • Leading blocklist vendors like Spamhaus, SpamCop,, and BitDefender provide the most trusted lists.
  • Effective implementation requires careful integration at multiple points, smart policies, and automatic list updates.
  • Monitor blocklist status closely and follow proper removal processes if unfairly listed.
  • Combine carefully managed allowlists with blocklists to optimize security while avoiding false positives.
  • Emerging AI-enhanced blocklists will provide faster, more sophisticated protection in the future.
  • Beyond email, DNS blocklists are evolving to secure web traffic, endpoints, cloud apps, and entire networks.

By leveraging carefully curated and implemented DNS blocklists, organizations can cost-effectively enhance threat protection across attack surfaces while reducing manual security workloads.

Frequently Asked Questions About DNS Blocklists

Q: What are the main types of DNS blocklists?

A: The three most common are IP-based blocklists, domain-based blocklists, and hash-based blocklists. These list different indicators associated with threats.

Q: How often are DNS blocklists updated?

A: Leading blocklist vendors update their lists multiple times per day, or even hourly, as new threats emerge. Organizations should configure automatic updates.

Q: Can I get accidentally blocklisted even if I follow best practices?

A: Unfortunately yes – false positives happen on occasion. Monitoring blocklist status and having a removal process is key.

Q: What’s the difference between DNSBLs and RBLs?

A: DNSBLs rely on historical DNS data, while RBLs operate in real-time. But the terms are often used interchangeably.

Q: Where can I download reputable blocklists for free?

A: Vendors like Spamhaus offer free trial access to test their blocklists. Open-source lists like Squidblacklist also exist.

Q: Should I merge every free blocklist I find into one mega-list?

A: No – small lists of questionable accuracy can do more harm than good. Focus on a few well-maintained lists from reputable sources.

Q: How do I configure blocklists on my email server or network?

A: Consult your platform’s documentation. Usually there are simple controls to enable blocklist filtering and configure exceptions.

Q: What should I do if a blocklist is incorrectly blocking legitimate emails?

A: First add the domain or IP to your whitelist. You can then contact the blocklist vendor to request removal of the false positive.

Q: Is it safe to publicly post a blocklist removal request?

A: No. Removal requests often include API keys or identifying information that should be sent directly to the blocklist vendor.

Q: Can DNS blocklists protect against advanced threats like zero days?

A: Blocklists focus on known threats. But when integrated into a robust security stack, they provide an important layer of protection.