What open 'bad domain' lists can I use to filter newsletter subscriptions from typo domains?

Key findings

• Distinction: General spam blocklists are distinct from lists targeting malicious typo domains. Spam blocklists often focus on IP addresses or domains known for sending unsolicited bulk email, whereas typo domains specifically mimic legitimate ones to trick users.
• Disposable domain lists: Several open-source lists, often found on platforms like GitHub, catalog disposable email domains. These are useful for blocking temporary or throwaway addresses, but may not cover typo-squatted domains.
• Limitations: Malicious typo domains like gmai.com can be challenging to block using simple lists because they often possess valid MX records and may even simulate engagement by opening opt-in links.
• Programmatic challenges: Identifying and blocking these types of domains programmatically is difficult, particularly for email service providers (ESPs) that rely on more general blocklists or reputation scores.
• List hygiene tools: Email list hygiene services can help identify problematic addresses, but they must balance verifying good addresses with the risk of inadvertently aiding spammers in avoiding spam traps.

Key considerations

• Implement double opt-in (DOI): This is a fundamental step to validate email addresses and ensure genuine interest, significantly reducing the impact of bad signups, including those from typo domains. Learn more about strategies for email list validation.
• Leverage specialized services: Consider email validation services that go beyond simple syntax checks to identify known disposable or problematic domains. This aids in removing bad email addresses from your list.
• Monitor engagement: While some typo domains may show initial engagement, a lack of sustained, meaningful interaction can be an indicator of a problematic address. Analyze patterns like immediate opens followed by no further activity.
• Typosquatting awareness: Understand the concept of typosquatting, where attackers register domain names that are common misspellings of legitimate ones. This helps in proactively identifying potential threats to your subscriber list. For more, see the NoSpamProxy explanation of typosquatting.
• Form-level suggestions: Consider implementing a system on your signup forms that suggests corrections for common domain typos without auto-fixing them, allowing users to correct legitimate mistakes.

Key opinions

• Focus on list hygiene: Many marketers identify 'list hygiene' as the primary strategy for combating bad email addresses, including those from typo domains. Utilizing services that validate emails at signup time is a common recommendation.
• Leveraging existing lists: There's a recognition that open-source lists on GitHub or similar platforms can be valuable for filtering disposable email domains (e.g., yopmail). Some marketers also point to compiled lists like Darkmail.domains which combine various sources of bad domains.
• Difficulty with active typos: A key concern for marketers is how to block typo domains (like gmai.com) that have valid MX records and actively engage with opt-in links, as these are not typically caught by standard disposable email lists.
• Beyond deliverability: Some suggest that if a domain never successfully delivers or shows zero sustained engagement, it might be better to simply ignore those signups, even if a direct blocklist isn't available.
• Engagement patterns: Marketers recognize that distinguishing legitimate engagement from automated opens (e.g., corporate email scans) or immediate, one-off interactions is difficult without granular reporting.

Key considerations

• Utilize email validation services: Marketers should consider integrating services that check for typos, syntax errors, and known fake or disposable addresses to maintain a clean list. This directly impacts domain reputation.
• Double opt-in importance: Emphasize implementing double opt-in to ensure subscribers genuinely want to receive emails, as this is a robust defense against various forms of bad signups, including typo domains.
• Form-level validation: While auto-correcting is discouraged, providing suggestions for common typos at the point of signup can help users submit accurate email addresses and reduce accidental bad data.
• Engagement monitoring: Develop strategies to identify suspicious engagement patterns, such as immediate opens followed by no subsequent interaction, which might indicate a spamtrap or malicious activity. This is key to identifying suspicious email domains.
• Proactive email list cleaning: Regularly clean your email lists to remove inactive subscribers, hard bounces, and any addresses identified as problematic, as highlighted by Moosend's recommendations for email list cleaning.

Key opinions

• List hygiene is key: Experts consistently point to list hygiene as the foundational element, suggesting that providers can validate emails at the point of signup to prevent problematic addresses from entering a list.
• Typos are complex: Blocking a typo domain like gmai.com is difficult because it may not appear on typical disposable domain lists. This often requires checking MX records or other advanced programmatic methods, which are not always feasible for all senders.
• Spamtrap dilemma: There's a delicate balance between helping users block bad addresses and inadvertently providing information that helps malicious actors avoid spam traps. Providers are hesitant to publish data that could be exploited.
• Manual solutions: Some technical experts use custom scripts to identify and block domains that host parked domains or exhibit suspicious MX record behavior, indicating potentially malicious intent.
• Confirmed opt-in: Confirmed or double opt-in is consistently emphasized as a crucial protection mechanism, as it ensures genuine subscriptions and deters those attempting to use typo domains maliciously.

Key considerations

• Robust validation at signup: Rely on comprehensive email validation services during the subscription process. These can identify not only syntax errors but also known disposable domains and potentially problematic patterns, which contributes to blocking disposable email domains.
• Understand spamtrap mechanics: Be aware that some email addresses, even if they show initial engagement, might be spam traps. Providers of email validation tools must navigate the ethical line of not assisting bad actors in avoiding these traps. For more on this, see what spam traps are and how they work.
• Implement double opt-in (DOI): This is a critical best practice that acts as a strong barrier against invalid or malicious signups, confirming genuine subscriber intent. Twilio discusses avoiding email blocklists by maintaining list hygiene.
• Custom blocking rules: For advanced users or those running their own mail transfer agents (MTAs), implementing custom rules to block specific IP addresses found via MX lookups for suspicious typo domains can be effective, though not easily scalable for all senders.
• Reputation monitoring: Keep an eye on unusual domain or IP activity, especially if you notice patterns that resemble tactics used by bad actors to identify suspicious email domains.

Key findings

• Blocklist definitions: Email blocklists (also known as blacklists) are widely defined as records of IP addresses or domains identified as sources of spam or other unwanted emails, used by servers to filter incoming messages.
• Reasons for bad data: Documentation points to various factors contributing to bad email list data, including typos, syntax errors, and the use of fake or disposable email addresses.
• Typosquatting explained: Typosquatting is a recognized form of cybercrime where attackers register domain names intentionally similar to well-known sites, relying on user typos for traffic or malicious activities.
• Suppression lists: Email platforms often maintain both global suppression lists (based on known bad domains) and custom suppression lists (editable by users) to manage email health.
• Multi-RBL services: Resources often mention services like MultiRBL, which aggregate data from various DNS blocklists (DNSBLs), allowing for comprehensive checks of IP addresses or domains against multiple blacklists.

Key considerations

• Understand blocklist function: Familiarize yourself with how email blocklists operate and their role in spam filtering. This knowledge is crucial for understanding why certain domains might be flagged. See Campaign Monitor's explanation of email blacklists.
• Prioritize data quality: Recognize that issues like typos and fake addresses are primary reasons for poor email list data. Implementing robust validation from the outset can prevent many deliverability problems. More on reasons why email list data goes bad is available.
• Leverage suppression lists: Utilize existing global and custom suppression lists provided by your email platform to block known bad domains and those you identify as problematic. Bloomreach documentation offers insights into managing email health through suppression lists.
• Continuous vigilance: Maintaining email health requires ongoing effort, including regularly monitoring lists and adapting strategies to counter evolving threats like typosquatting. For general guidance, consider which email domains marketers should avoid.