---
title: "Everything You Need to Know About DNS Blocklist | DMARC Report"
description: "Everything You Need to Know About DNS Blocklist from DMARC Report explains practical steps for email authentication, domain protection, deliverability, and."
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---
Quick Answer
Everything You Need to Know About DNS Blocklist Everything You Need to Know About DNS Blocklist /! This file is auto-generated / !function(d,l){"use strict";l.querySelector&&d.addEventListener&&"undefined"!=typeof URL&&(d.wp=d.wp||{},d.wp.receiveEmbedMessage||(d.wp.receiveEmbedMessage=function(e){var t=e.data;if((t||t.secret||t.message||t.value)&&!/\[^a-zA-Z0-9\]/.test(t.secret)){for(var s,r,n,a=l.querySelectorAll('iframe\[data-secret="'+t.secret+'"\]'),o=l.querySelectorAll('blockquote\[data-secret="'+t.secret+'"\]'),c=new RegExp("^https?:$","i"),i=0;i ' title="Embed Code" class="input-embed input-embed-10639" readonly/> Have you ever wondered how mail servers keep track of suspicious domains or IP addresses and prevent their messages from entering your mailbox? With grave cyberattacks.
Related: [Free DMARC Checker](/tools/dmarc-checker/) ·[How to Create an SPF Record](/tools/spf-record-generator/) ·[SPF Record Format](/blog/spf-format-checker-dos-and-donts-for-email-authentication/)
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> The engineering challenge with DMARC at scale is report volume, not complexity, says Brad Slavin, General Manager of DuoCircle. A domain that sends 100,000 emails per day generates dozens of aggregate report files daily from different receivers. Parsing, classifying, and trending that data is why DMARC Report exists.
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Have you ever wondered how mail servers keep track of suspicious domains or IP addresses and prevent their messages from entering your mailbox? With [grave cyberattacks](https://www.bleepingcomputer.com/news/security/the-biggest-cybersecurity-and-cyberattack-stories-of-2023/) like \*\*phishing, spoofing, and ransomware being at an all-time high, it is crucial for all the stakeholders in digital communication to prioritize [email security](https://dmarcreport.com/blog/why-email-security-matters-and-how-to-get-it-right/).
To keep your email ecosystem safe and secure, email servers employ various methods to ensure your inboxes remain free from **spam and malicious content**. One of them is the use of [DNS-based blocklists or DNSBL](https://en.wikipedia.org/wiki/Domain%5FName%5FSystem%5Fblocklist). _DNS blocklists are comprehensive \*\*lists of IP addresses and domain names that have been flagged for sending fishy (or is it phish-y) messages_.
But there’s more to these lists than this! If you’re wondering what exactly DNSBLs are and why they are so important in the context of **maintaining secure communication**, you’re in the right place!
In this article, we’ll explore everything you need to know about these lists, covering everything from how they work, what is the impact of being on DNSBLs and the \*\*best practices to avoid landing on these lists.
## What is a DNS Blocklist?
A DNS blocklist is not a tool but \*\*a mechanism employed by system moderators to block out [malicious emails](https://www.moneycontrol.com/news/business/email-attachments-from-bonafide-ids-can-be-malicious-government-alerts-officials-11229511.html) or spam by maintaining a directory of the locations on the internet that have a reputation for sending spam emails. _As the name suggests, these lists are based on the Domain Name System (DNS) that converts complicated IP addresses into easy-to-remember domain names._ So, if a domain name falls into the “bad books” of a DNSBLs maintainer, the server will be blacklisted, and all the messages received from the domain will either be \*\*flagged as spam or rejected altogether.
_Another thing that you should know about DNS blocklists is that there are many DNSBLs out there, and they rely on extensive criteria to list and delist addresses from the blocklist_. The factors that these specific blocklists take into consideration include \*\*ISPs that host spammers \*\*or those that send spam to a [honeypot system](https://www.geeksforgeeks.org/what-is-honeypot/), [zombie computers](https://www.pandasecurity.com/en/security-info/zombie/), etc.
## How Does it Work?
DNS blocklists keep an eye out for certain **red flags in your emails**. Whether your domain has a not-so-good reputation , there’s been a sudden surge in the number of emails that you sent, or the content of the emails looks suspicious , all these factors can raise eyebrows. Further, email clients like Gmail and [Outlook](https://dmarcreport.com/blog/microsoft-outlook-rolls-out-its-new-authenticator-lite-feature-for-ios-and-android-users/) pick this information from the DNS blocklists, align it with their internal metrics and then **decide the fate of the message** \- whether it will be delivered or blocked.
## What Happens if You End Up On the Blocklist?
Being on the internet’s defaulters’ list can severely hurt your business in more than one way. _As we have already established earlier, one of the immediate implications of being on the DNS blocklist is **poor email deliverability**_.\_ \_If your domain or IP address is on a DNSBL, even your \*\*legitimate emails will be rejected by the server or redirected to the [spam folder](https://www.ccleaner.com/knowledge/what-is-a-spam-folder-and-what-is-junk-mail).
Moreover, being on the blocklist can also taint a **business’s reputation**, especially if most of your emails end up in their spam folders. In essence, being on a DNS blocklist is more than a mere inconvenience; it’s a significant hurdle that affects everything from **communication to reputation**, [brand integrity](https://www.channelsight.com/blog/brand-integrity), etc.
Bear in mind that being on a \*\*random blocklist on the internet does not cause any problems as such. It is only when you land up in some of the reputable ones that you notice major [email deliverability](https://dmarcreport.com/blog/what-is-a-dmarc-policy-and-how-does-it-affect-sending-my-emails/) woes, along with other consequences.
## How Do You Avoid Being Put on the Blocklist?
Being off the DNS blocklist is \*\*an ongoing challenge that most enterprises face, especially considering the impact it can have on your business. While it seems daunting, it is very much possible to stay out of the bad books and maintain your brand integrity. To ensure that your domain does not end up in the DNS blocklist, you should follow a combination of **good practices**, vigilance, and a proactive approach to managing your [email infrastructure](https://dmarcreport.com/blog/dmarc-office-365-complete-setup-guide-2026/).
Here’s how you can do it:
## Know Your Sending Servers
If you want to avoid being put on the blocklist, make sure that you’re aware of your sending practices, with special attention to factors like sending emails from [shared mail servers](https://www.scalahosting.com/blog/what-is-shared-email-hosting/#:~:text=Shared%20email%20hosting%20is%20a,messages%20of%20many%20other%20clients.%20.). Using a shared mail server can do you **more harm than good**. \_If one of the users engages in practices that lead to blacklisting (like sending spam), it can affect everyone else using that same IP\_.
## How Do You Avoid Sending Large Emails?
As much as you’d want to incorporate maximum information in your email, you should refrain from doing so! If your **email size is bigger than usual**, chances are it will be [marked as spam](https://www.cakemail.com/blog/post/the-complete-guide-to-avoid-being-marked-as-spam). To prevent the possibility of DNS blocklisting, check your \*\*HTML email template to ensure your code is optimized .
## Check Your Email Content
The way you craft your emails also contributes to the blocklisting of your domain. So, when you curate your emails, \*\*avoid using spam-like content in your emails. This includes overly promotional language, that is, phrases like “ Buy Now” and “Apply ”; excessive use of caps or exclamation marks, and suspicious links. Remember, [effective email communication](https://www.flowrite.com/blog/effective-email-communication) is about **creating value for the recipient**, not just broadcasting your message.
## Prioritize Email Authentication
_One of the most reliable and efficient ways to ensure that your email communication is secure is by implementing an email authentication strategy_. By implementing standards like [SPF](https://dmarcreport.com/what-is-spf/) (Sender Policy Framework), [DKIM](https://dmarcreport.com/what-is-dkim/) (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance), you establish a \*\*verification system that authenticates your emails, proving they are from a trusted source.
If you’re committed to **safeguarding your email ecosystem and preventing your IP addresses from showing up on the DNS blocklist**,\*\* it is high time you make [email authentication](https://dmarcreport.com/blog/why-email-security-matters-and-how-to-get-it-right/) a priority!
Want to know how [DMARC](https://dmarcreport.com/) can help you meet your email security goals? Speak to one of our \*\*experts at DMARCReport or [book a demo](https://dmarcreport.com/book-a-demo/) today!
## Topics
[ dkim ](/tags/dkim/)[ DMARC ](/tags/dmarc/)[ email security ](/tags/email-security/)[ SPF ](/tags/spf/)
[ Adam Lundrigan ](/authors/adam-lundrigan/)
CTO
CTO of DuoCircle. Leads engineering for DMARC Report and DuoCircle's email security product portfolio.
[LinkedIn Profile →](https://www.linkedin.com/in/adamlundrigan/)
## Take control of your DMARC reports
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## Related Articles
[ Foundational 8m 10 Critical Learnings From Verizon’s 2021 DBIR - A DMARCReport Perspective Nov 25, 2025 ](/blog/10-critical-learnings-from-verizons-2021-dbir-a-dmarcreport-perspective/)[ Foundational 12m 10 DNS Blacklist Insights That Improve Email Security And Deliverability Fast Nov 14, 2025 ](/blog/10-dns-blacklist-insights-to-improve-email-security-and-deliverability/)[ Foundational 12m 10 Email Spoofing Detection Tools That Dramatically Improve Brand Protection Nov 11, 2025 ](/blog/10-email-spoofing-detection-tools-that-dramatically-improve-brand-protection/)[ Foundational 12m 10 Reasons SPF Filtering Is Critical For Email Security Nov 19, 2025 ](/blog/10-reasons-spf-filtering-is-critical-for-email-security/)
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