What open 'bad domain' lists can I use to filter newsletter subscriptions from typo domains?
Michael Ko
Co-founder & CEO, Suped
Published 10 May 2025
Updated 16 Aug 2025
7 min read
Maintaining a clean email list is fundamental to successful deliverability. One of the less obvious but equally damaging threats to your email sender reputation comes from typo domains. These are domains that mimic legitimate ones but contain slight misspellings, like gmai.com instead of gmail.com. They often act as spam traps, quietly eroding your sender score and leading to messages being blocked or sent to the spam folder.
While there are many general email blocklists that target known spammers or malicious IP addresses, finding comprehensive open bad domain lists specifically for filtering typo domains from newsletter subscriptions can be a challenge. These aren't always explicitly labeled as such, as their primary function is often to ensnare senders with poor list hygiene. We will explore how to identify and mitigate these risks effectively.
The challenge of typo domains and spam traps
Typosquatting, or URL hijacking, is the practice of registering domains that are common misspellings or variations of legitimate brand names. The goal is to profit from user typos, often leading to phishing, malware distribution, or, in our case, setting up typo spam traps. These email addresses appear active and might even engage with your initial opt-in emails, but they are designed to flag senders who collect addresses incorrectly.
The problem with these addresses is that they often have valid MX records and can even complete a double opt-in process. This makes them incredibly difficult to detect using standard validation methods that primarily check for syntax or known disposable domains. You might send an opt-in link, it gets clicked, and then you find your domain reputation taking a hit later on as these addresses complain or simply don't engage with subsequent emails.
Unlike typical spam addresses that might bounce or have no MX records, typo domains often masquerade as legitimate recipients. This means they contribute to a higher spam rate and lower engagement metrics, signaling to mailbox providers that your sending practices might be questionable. It's a subtle but significant form of domain reputation degradation.
Understanding typo spam traps
Typo spam traps are designed to catch senders who collect email addresses without proper verification. They are variations of legitimate domains, like gmaii.com instead of gmail.com. Even with double opt-in, if a user misspells their address, your emails could still hit a trap.
The risk to sender reputation
Consistent hits on typo spam traps can severely damage your domain reputation. Mailbox providers interpret these as signs of poor list acquisition practices, leading to your legitimate emails being sent to spam folders or even being outright rejected. This affects your overall email deliverability.
Available open source lists for filtering
When looking for open lists to filter typo domains, you'll primarily find resources related to disposable email addresses (DEAs). These lists are valuable for preventing sign-ups from temporary or throwaway email services, which are often used for abuse or to avoid real engagement. While not specifically for typos, preventing DEAs is a crucial part of overall list hygiene.
Several open-source GitHub repositories compile extensive lists of disposable email domains. These lists are maintained by communities and can be integrated into your signup forms or backend processes to block registrations from these known problematic sources. Some prominent examples include the ivolo/disposable-email-domains and the disposable-email-domains/disposable-email-domains repositories.
While useful, these lists typically focus on known disposable services rather than subtle typos of major email providers. For example, a domain like gmai.com might not appear on a standard disposable email list because it's not a service; it's a typosquatted domain. You can also explore combined lists like Darkmail.domains, which aggregates data from various sources.
List Type
Primary Use Case
Examples
Disposable email lists
Prevent sign-ups from temporary email services and deter abuse. Useful for initial list cleaning during subscriptions.
mailinator.com, yopmail.com, temp-mail.org
DNS-based blocklists (DNSBLs)
Block email from IP addresses or domains known for sending spam or malware. Primarily used by email servers to filter incoming mail.
Identify email addresses created from common misspellings of popular domains specifically to catch senders with poor hygiene or scraped lists.
gmai.com, hotmial.com, yhaoo.com
Beyond open lists: strategies for identifying problematic domains
Since direct open lists for typo domains are rare, you'll need to employ additional strategies. One approach is to programmatically check the MX records of newly subscribed domains. Typosquatted domains often have unusual or unexpected MX records, sometimes pointing to generic hosting providers or servers known for parked domains, rather than the mail servers of the legitimate service.
For example, while gmail.com has specific mail servers, gmai.com might point to a generic Amazon Web Services (AWS) IP address or another cloud provider. This is a strong indicator of a suspicious domain. You could build a script that performs MX lookups for new sign-up domains and flags those with generic or unexpected MX records. This requires custom development or integration with a dedicated email validation service.
Python script to check MX records for a domainpython
import dns.resolver
def check_mx_records(domain):
try:
answers = dns.resolver.resolve(domain, 'MX')
mx_records = [str(rdata.exchange) for rdata in answers]
return mx_records
except dns.resolver.NoAnswer:
return []
except dns.resolver.NXDOMAIN:
return ['NXDOMAIN'] # Domain does not exist
except Exception as e:
return [f'Error: {e}']
# Example usage:
mx_gmai = check_mx_records('gmai.com')
mx_gmail = check_mx_records('gmail.com')
print(f"MX records for gmai.com: {mx_gmai}")
print(f"MX records for gmail.com: {mx_gmail}")
Another strategy involves behavioral analysis post-subscription. If an email address shows immediate, automated opens but no subsequent genuine engagement (e.g., clicks on multiple different links over time, replies), it could be a sign of a spam trap or a bot. While some corporate email scanners might mimic this behavior, a pattern of only immediate opens coupled with no long-term interaction is suspicious. This type of analysis is part of broader suspicious email domain identification efforts.
The importance of list hygiene and validation
The most effective way to combat typo domains and ensure list cleanliness is through robust email list hygiene practices, starting at the point of subscription. Even with double opt-in, human error leads to typos. Implementing real-time email validation on your signup forms is essential. These services can automatically detect invalid syntax, known disposable domains, and often suggest corrections for common misspellings.
Many email validation tools use proprietary data sets that include typo domains and spam trap indicators. While these aren't always open lists, they leverage extensive data to protect your sender reputation. Consider using a service that offers a disposable email check and email list cleaning to ensure you're reaching real, engaged subscribers.
Reactive approach: monitoring and removal
Blocklist Monitoring: Regularly check major blocklists for your IP and domain. While not directly for typos, getting listed often stems from poor list quality, including typo traps.
Engagement Analysis: Segment or suppress subscribers with consistently low or no engagement. This can passively remove potential traps. Refer to your Google Postmaster Tools data.
Proactive approach: validation and prevention
Real-time Validation: Integrate an email validation API at the point of subscription. Tools like ZeroBounce or Kickbox can detect invalid formats and common typos.
Double Opt-in (DOI): Always use double opt-in for new subscriptions. This confirms the email address is valid and the subscriber genuinely wants your content, significantly reducing the risk of hitting typo traps. It's a key best practice for email deliverability.
No single open blocklist will perfectly filter all typo domains, as these are often dynamic and context-dependent. A multi-layered approach combining prevention at signup, regular list hygiene, and behavioral monitoring is key to protecting your sender reputation and ensuring your messages reach the inbox. Continuous monitoring of your metrics, such as spam complaints and bounce rates, is also essential for early detection of issues.
Views from the trenches
Best practices
Implement real-time email validation on all subscription forms to catch invalid or misspelled domains immediately.
Always use a double opt-in process, even if it adds an extra step for subscribers, to confirm genuine interest.
Regularly monitor engagement metrics (opens, clicks) for suspicious patterns, especially immediate opens without further interaction.
Perform periodic email list cleaning to remove inactive subscribers and potential spam traps that might have slipped through.
Common pitfalls
Relying solely on open disposable email lists, as these often miss clever typos of legitimate domains.
Not checking MX records for new sign-ups, which can reveal parked domains used for typosquatting.
Ignoring low engagement from certain segments, as this could indicate hidden spam traps affecting your overall deliverability.
Automatically correcting email typos in forms, which can inadvertently send emails to spam traps or incorrect recipients.
Expert tips
Aiverson from Email Geeks says: Consider that if receiving domains have reputation, so should senders. If you consistently fail to deliver or see zero engagement from certain sign-ups, it might be best to ignore or suppress those addresses.
Tvjames from Email Geeks says: Blocking domains with MX records pointing to generic cloud IPs, like those from AWS that host parked domains, could be a programmatic way to identify and prevent sending to typo addresses.
Wise Laura from Email Geeks says: While open lists are useful, the most robust approach often involves paid list hygiene services that can validate addresses at signup time and identify 'throwaway domains'.
Tvjames from Email Geeks says: Creating a list to identify typo variants could be valuable for the community, but it's important to be careful not to reveal active spam traps which could then be exploited by bad actors.
Marketer view
Marketer from Email Geeks says: I found that Kickbox's API is backed by GitHub data, specifically the `ivolo/disposable-email-domains` repository. Another useful dataset is at `disposable-email-domains/disposable-email-domains`, which includes usage examples in various programming languages.
2022-04-24 - Email Geeks
Marketer view
Marketer from Email Geeks says: The `darkmail.domains` website aggregates a large collection of bad emails and domains from various GitHub sources, which is also a good resource for filtering.
2022-04-25 - Email Geeks
Summary of strategies
Filtering newsletter subscriptions from typo domains requires a strategic blend of proactive validation and reactive monitoring. While truly "open" lists for typo domains are uncommon due to their nature as spam traps, leveraging disposable email lists and implementing robust real-time validation at the point of entry are your best defenses.
Continuously reviewing your list for low engagement, unexpected MX records, and maintaining a strict double opt-in policy will help protect your sender reputation and ensure high email deliverability. Remember, a clean list is the foundation of effective email marketing, and preventing problematic sign-ups is far easier than recovering from a damaged reputation.
Spamhaus
