Email Blocklists: How They Work & How to Get Off

In 2022, nearly 45% of all emails sent were spam. Although global blocklists are helping maintain a healthy email practice worldwide, they can be nightmares for (legitimate) email marketers. 

If you don’t know what blocklists are or how to remove yourself (IP address or domain) if you get listed in one, your carefully crafted email campaigns will fail. 

So, how can you effectively stay out of blocklists and maintain high email deliverability for your business? 

In this blog post, you’ll learn about global blocklists, how to avoid blocklisting, and what measures you can take to remove yourself from them. 

What is an Email Blocklist? 

Email blocklist (AKA email blacklist) is a real-time list of domains or IP addresses that are identified and flagged by spam filters for sending spam. 

Internet Service Providers (ISPs), anti-spam vendors, and free mailbox providers extensively use the blocklists to maintain their systems spam-free. ESPs (email service providers), individuals, or businesses can check the email blocklists to see if their IP address or domain is blocklisted. Depending on the quality of your email or the email list you are sending to, you may find your IP or domain blocked in several email blocklists. 

In short, a blocklist is a barrier between your organization and your email recipients. Although a few blocklists (e.g., Spamhaus) may significantly impact your email deliverability, guaranteeing high email open rates is the key to success in email marketing. Most major Internet Service Providers (ISPs) maintain their own internal blacklists, while others rely on publicly accessible blocklists.

Different Types of Email Blocklists

Two major blocklists are commonly used: IP-based blocklisting and domain-based blocklisting. Each type serves a distinct purpose in identifying and preventing potentially harmful senders.

IP-based Blocklisting

Every computer, server, or device connected to the internet is assigned a unique IP address. IP-based blocklisting categorizes and restricts email traffic based on the originating IP address of the sender's server. When a particular IP address is detected to be sending spam emails or potentially malicious content, it is subjected to IP-based blocklisting.

Key characteristics of IP-based blocklisting include:

• IP-based blocklisting targets specific IP addresses that are used for sending spam emails.
• When a particular IP address sends spam emails frequently, it might get listed in a blocklist.
• To prevent further abuse or scams, if spam reports originate from a particular IP address or a defined range of IP addresses, the entire range may be blocklisted.
• Once an IP address is blocklisted, emails originating from that address are filtered out as spam until the issue is resolved. 

Domain-based Blocklisting

A domain is the part of an email address after the "@" (e.g., smartlead.ai in "sattwik@smartlead.ai"). Domain-based blocklisting works on a specific sender's domain, irrespective of the IP addresses used for sending emails. A domain is blocklisted when it's reported for sending large volumes of spam emails.

Key characteristics of domain-based blocklisting include:

• Domain-based blocklisting focuses on the sender's domain name despite the IP addresses used.
• Even if a sender switches to a different IP address, if their domain remains blocklisted, their emails will continue to be rejected or filtered as spam.
• Senders who try to bypass IP-based blocklists by changing their sending infrastructure are more likely to get their domain blocklisted. 
• If your domain is blocklisted, it will hamper your email-sending efforts.  

Companies Hosting Email Blocklist Services

Several companies offer email blocklist services, each with varying levels of impact:

1. Spamhaus: A prominent and impactful blocklist provider with both automated and human-reviewed lists. Being listed on Spamhaus can suspend email activities until resolved.

2. SpamCop (owned by Cisco): Lists suspicious IPs for 12 to 48 hours or longer for recurring spam issues. Users can request delisting.

3. SORBS (owned by Proofpoint): This medium-to-low-impact blocklist lists IPs for a minimum of 48 hours, potentially longer for high spam volume. Recurrent listings prompt senders to address issues.

4. UCEProtect: It is a low- to no-impact German-based blocklist. It's less widespread, and IPs listed face a minimum 7-day listing. Some view it as suspicious due to donation requests for removal.

Read more: UCEPROTECTL3 Blacklist: All You Need to Know + How to Remove Yourself

5. MagicMail/Linux Magic/MIPSpace: MIPSpace blocklists focus on bulk email traffic, but only non-bulk senders can delist. MagicMail users have limitations in marking senders as "safe."

6. Invalument: Offers three unique blacklists (ivmURI, ivmSIP, ivmSIP/24) with diverse information like IP addresses and domains.

How Email Blocklists Work: Understanding the Mechanism

Email blocklists extensively use spam traps to identify spam senders. Spam traps are strategically deployed email addresses used to lure in and identify senders with dubious intentions. 

There are three types of spam traps: 

1. Recycled Spam Traps

Recycled spam traps were once valid and active email addresses used by legitimate users. Once these accounts become dormant, receiving servers often refuse or bounce messages sent to these addresses for usually a year or more to catch senders who persistently target defunct email addresses. After this dormancy, these email accounts are reactivated as spam trap addresses. Having recycled spam traps in email lists raises concern over list acquisition practices and poor list maintenance. 

2. Typo Traps

Typo traps exploit human errors by including email addresses likely to be typo errors in the recipient lists. For example, you might accidentally send an email to "abc@hitmail.com" instead of "abc@hotmail.com." Sending too many emails to typo traps indicates questionable list acquisition practices and a lack of list hygiene.

3. Pristine Traps

ISPs and anti-spam organizations intentionally fabricate email addresses and domains to use them as spam traps. Pristine traps are designed solely to identify spammers. When a sender purchases or scrapes email addresses from third-party vendors, pristine traps make their way into the mailing lists. Sending a considerate number of emails to pristine traps might get your IP blocklisted. 

However, blocklists do not entirely rely on spam traps. Some blocklists list domains and IP addresses based on user-generated feedback and manual reporting. This user-centric approach keeps the blocklists up-to-date.

How Do You Land in Email Blocklists?

Understanding why you might end up on an email blocklist is essential to ensure a high deliverability of your campaigns and maintain a high sender reputation.

1. Sending to Spam Traps

Spam traps are dormant/inactive email addresses deployed by ISPs or blocklist operators to catch senders spamming email users’ inboxes. Sending to spam traps means the sender didn’t indulge in double opt-in practices or maintain proper list hygiene. Sending a campaign to a high number of spam traps can get your domain or IP address blocklisted. 

2. High User Complaints

When recipients mark your emails as spam or use the "Report Spam" button, it signals that your messages are unwelcome or irrelevant. High user complaint rates can occur for various reasons, such as sending emails to recipients who didn't opt-in, sending emails too frequently, sending irrelevant content, or neglecting list hygiene practices. A surge in spam complaints can prompt ISPs to block your sending domain or IP address to protect their users from unwanted emails.

3. Sending to a High Number of Inactive Email Accounts

When you send emails to a significant number of inactive email addresses, you are likely to experience hard bounces. Hard bounces happen when an email cannot be delivered because the recipient's address is incorrect, no longer exists, or their (recipient’s) mailbox is full. High hard bounce rates indicate to ISPs that your email list may contain outdated or improperly acquired addresses.

4. Rapid List Growth

A healthy email list grows organically over time as more and more new subscribers opt into your mailing list. However, if your list experiences sudden growth, ISPs may get suspicious. ISPs suspect the list has been purchased, scraped from the internet, or obtained non-consensually. Rapid increases in sending volume can also identify the sender as a spammer. 

Your email usually goes through some tests to check whether it will be sent to the inbox or the spam folder. To understand when a blocklist interacts with an email, take a look at this graphic: 

When you send an email (sender), the message is received by the Internet Service Provider (receiver), and the ISP decides to send your email either to the inbox or the spam folder. If the ISP has a blocklist, it will run your IP address or domain through it. 

How Do You Know If You Are on a Blocklist? 

1. Use Online Blocklist Checkers

You can visit websites like Spamhaus, Spamcop, Passive Spam Block List (PSBL), Invaluement, SenderScore, Barracuda, etc. 

For instance, Spamhaus offers an IP address and domain name lookup tool. By entering your IP address or domain name into the checker, you can check whether your IP address or domain is blocklisted.

2. Leverage Email Service Providers

Your email service provider (Outlook, Gmail, etc.) can help you identify if you are listed on any blocklists. Many ESPs, such as Mailgun, offer blocklist monitoring services. These services automate the process of checking whether your IP address or domain has been blocklisted across multiple blocklists. 

3. Pay Attention to Error Messages

When you send emails to your contact list and see error messages bouncing back, that’s your point of concern. Error messages contain valuable information regarding blocklist issues. These messages indicate blocklisting and may include a URL or reference to initiate the blocklist removal process. 

4. Monitor Regularly 

You can prevent your email address or domain from being blocklisted only with regular monitoring. Blocklist status changes due to various factors, including the quality of your email content and the behavior of your recipients. However, it is essential to maintain email hygiene best practices to stay away from blocklists altogether. 

How to Avoid Email Blocklists? 

Ensuring that your emails stay away from blocklists is crucial for the success of email marketing campaigns. As we’ve discussed before, email content and mailing lists are the primary factors for blacklisting. Here are key strategies to help you stay away from email blocklists:

1. Thoughtful Email Content

Irrelevant or repetitive content can lead to low engagement and potential spam reports.

Personalization and email list segmentation are the keys to offering tailored content. Craft personalized emails that are relevant to your subscribers. This shows your recipients that you understand their needs and preferences, significantly reducing spam reports and unsubscribes.

For example, if they signed up for product updates, sending them unrelated content can lead to increased spam complaints. Be mindful of how many and how often you send emails. A sudden increase in email frequency or sending to a significantly larger list can trigger concerns and might lead to blocklisting. 

This is where Smartlead’s automated email warmup comes in. It maintains natural human activity for sending emails. Smartlead’s algorithm gradually ramps up the number of emails and manages smart replies to maintain high email deliverability and sender reputation. 

2. Monitor Email Campaign Statistics

Besides tracking email open rates and click-through rates, keep an eye on domain-specific email open rates. If you see a significant drop in opens from a particular domain, it might be an issue with your email delivery.

Check your blacklist status regularly using reputable blacklist monitoring tools, such as MxToolbox or HetrixTools. This way, you can identify and address any blocklisting issues promptly without hampering your email marketing campaigns or cold outreach campaigns.

3. Maintain High-Quality Email Lists: Build Your Own List

Avoid buying or scraping email lists; they're often outdated and lead to spam issues. Build your own list organically. Remove bounced, outdated, and unengaged subscribers to maintain sender reputation. Segment your list by factors like location, purchase history, and demographics for targeted, relevant emails, reducing spam complaints and unsubscribes.

Understanding and Removing Your Email from Blacklists

Getting listed on a blocklist can seriously damage your email deliverability, causing your emails to bounce or land in recipients' spam folders. Let’s see how you can promptly identify blocklisting, address the issue, and request removal.

Diagnose the Problem

To resolve email blocklisting issues, start by diagnosing the problem. Identify the specific blacklists affecting your email deliverability using online tools like MxToolbox or ZeroBounce.

Next, assess the severity of the blacklisting. Determine if it's on a single low-impact list or multiple ones to understand the extent of the issue.

Investigate the reason for blocklisting, which can be technical or compliance-related. Common causes include a sudden surge in email volume, high spam complaints, poor email list hygiene, bad content resembling spam, or suspected malware in your email infrastructure.

Assess and Address the Root Cause

Before requesting email delisting, review your email-sending practices for compliance with anti-spam regulations like the CAN-SPAM Act and GDPR. Consider email source, permission-based marketing, and campaign frequency.

Examine email content to ensure relevance and value while avoiding suspicious or malicious elements that trigger spam filters. Steer clear of spam-triggering words like 'Make $,' 'Earn,' 'Free,' and 'Fast cash' in subject lines.

Implement email authentication protocols like SPF, DKIM, and DMARC for sender legitimacy. Evaluate your email infrastructure and security measures to prevent misuse.

Assess recipient engagement through metrics like open rates, click-through rates, and spam complaints. Low engagement signals campaign or content issues that could lead to blacklisting.

Set up feedback loops with ISPs to identify problematic campaigns and disinterested recipients when they mark your emails as spam. Address these issues before pursuing delisting to avoid recurrent blacklisting.

Request Delisting from the Blocklists

The delisting process varies for every email blacklist. Some blocklists ask for a formal request for delisting, while others automatically remove your domain after a specific time period. Here is how to find the delisting process for some common blacklists:

• Spamhaus: Visit the Spamhaus website, enter your IP address or domain in The Blocklist removal center, and follow the provided instructions for delisting.
• Microsoft: Visit the Microsoft delisting portal, fill out the required information, and submit the form for review by Microsoft's delisting team.
• Proofpoint: Look up your IP address at their Dynamic Reputation IP Lookup portal or contact Proofpoint's support team, providing the necessary details and following their instructions.
• Barracuda: Visit Barracuda's delisting portal, complete the form with the required information, and submit it for review.
• Cisco/IronPort: The delisting process for Cisco/IronPort may vary; visit their website for instructions or contact their support team.
• Invaluement: Visit the Invaluement website and follow the provided delisting instructions, which typically involve a request for necessary information.
• Spamcop: Visit the Spamcop website and follow their delisting instructions, which may involve submitting a request through their web interface or by email.
• SURBL: SURBL's delisting processes may vary; follow the instructions on its website or contact its support team.

When requesting delisting, provide all required information, such as your IP address and evidence of corrective actions. Monitor progress, check email deliverability post-request, and be patient, as the process may take time. Follow vendor guidelines for additional steps if needed. To prevent future blacklisting, maintain best practices and avoid past mistakes. Ongoing vigilance is crucial for consistent email deliverability.

Spam Laws You Need to Know

In the last two decades, many countries have enacted spam laws to control the influx of unwanted and potentially harmful emails. Let’s check out some of the spam laws in different regions you need to comply with: 

The CAN-SPAM Act (US)

The CAN-SPAM Act, enacted in 2003 in the US, regulates email marketing. It requires senders to obtain consent through opt-in forms before adding recipients to mailing lists. Emails must include a simple unsubscribe option. Subject lines must accurately represent the content, preventing deception. Senders must also provide a valid physical address in their emails.

UK Privacy Regulations

UK Privacy and Electronic Communications Regulations aim to prevent spam. Organizations must get consent for marketing emails, provide opt-out options, and promptly honor unsubscribe requests.

Canadian Anti-Spam Rules

Canada's Anti-Spam Regulation mandates consent for business emails and requires senders to identify themselves with contact information clearly.

Australian Spam Act 2003

The Spam Act 2003 in Australia requires consent, functional unsubscribe options, and clear sender identification, including the physical business address.

EU Privacy Directive

The EU's Privacy and Electronic Communications Directive harmonizes anti-spam measures. It emphasizes explicit consent, easy opt-out processes, and transparent sender identification.

Top 10 Insider Tips to Stay Away from Blocklists

The wait is worth it. Here are Smartlead’s insights and insider tips to stay away from blocklists and keep your deliverability and sender reputation high.

1. Verify Email Addresses

Before sending an email, ensure the accuracy and validity of your recipients' email addresses. Invalid or outdated addresses not only result in bounces but also damage your sender's reputation.

To prevent this, we recommend the following techniques:

• Use tools like ZeroBounce, Hunter.io, QuickEmailVerification, MailboxValidator, or TheChecker to verify email addresses in real-time.
• Send a confirmation email to recipients, requesting that they verify their email addresses by clicking a link or responding.
• Adhere to correct syntax for email addresses, including the proper use of symbols like "@" and ".com."

2. Always Use Double Opt-in

The double opt-in method confirms that the recipients are genuinely interested in receiving your emails. By implementing double opt-in forms, you can minimize the risk of sending emails to uninterested or reluctant recipients, reducing bounce and spam complaint rates.

By employing double opt-in, you also showcase your commitment to respecting recipients' privacy, developing trust, and increasing email engagement.

3. Limit Email Sending Frequency

Sending excessive email volume over a short period can lead to high complaint rates, potentially causing your IP address to be blocklisted. To maintain a healthy sender reputation, Smartlead recommends:

• Establishing a schedule: Set a consistent email sending schedule of different types of messages to manage recipient expectations.
• Segmenting your email list: Divide your list into smaller, targeted segments based on subscriber behavior and preferences.
• Providing an opt-out option: Give recipients the choice to unsubscribe or receive fewer emails.

4. Monitor Email Bounce Rates

Bounce rates, including soft and hard bounces, can indicate problems with email addresses. High bounce rates affect sender reputation and might lead to blocklisting. 

5. Monitor Spam Complaint Rates

High spam complaint rates are a risk to your sender reputation. By regularly checking spam complaint rates, you can ensure that your emails resonate with your audience, make improvements to your email campaigns, and boost deliverability and engagement.

6. Choose Email Service Provider Carefully

Choosing a reputable email service provider is a very important factor for avoiding email blocklists. 

7. Follow Anti-spam Laws

Comply with anti-spam laws, such as the CAN-SPAM Act and GDPR. Adhere to the rules to maintain fair email practices, maintain a positive sender reputation, and reduce the risk of blocklisting.

8. Use Tools for Email Denylist Checker

Leveraging tools like MxToolbox, Mail-Tester, or the Barracuda Reputation System allows you to monitor your email reputation and address spam-related issues promptly. These tools can help diagnose problems and provide recommendations for improving email deliverability.

9. Use a Reputable IP Address

Your email server's IP address plays an important role in email deliverability. Monitor your IP reputation, maintain a clean email list, authenticate your emails, and limit email volume to ensure your IP address remains reputable.

Smartlead offers unique high-delivery IP addresses for every campaign, so you can maintain typo-notch deliverability. 

10. Optimize Your Email Content

Customizing your emails and offering valuable content are critical strategies for avoiding spam complaints and increasing engagement. With Smartlead, you can spintax your email messages to increase engagement and bypass spam filters.  

Conclusion

Maintaining a healthy email deliverability and avoiding email blocklists are crucial for successful email marketing. Email blocklists, used to protect users from spam, can be a nightmare for legitimate email marketers. To steer clear of them, follow these key strategies:

• Create relevant and engaging email content for your subscribers.
• Keep an eye on campaign statistics, manage high-quality email lists, and avoid spam traps and user complaints.
• Be cautious with list growth to ensure it's organic and avoid rapid increases.
• Regularly monitor your email status using online tools and error messages.

If you end up on a blocklist, take these steps:

• Diagnose the issue's severity and root cause.
• Implement necessary corrections to your practices.
• Request delisting from the specific blocklists affecting you.
• Follow the provided guidelines for each blocklist.

Compliance with regional spam laws, such as the CAN-SPAM Act, UK Privacy Regulations, Canadian Anti-Spam Rules, Australian Spam Act 2003, and the EU Privacy Directive, is also essential. By following these guidelines and maintaining best practices, you'll ensure high email deliverability, boost sender reputation, and succeed in your cold emailing endeavors.