How can I identify and remove email addresses submitted via list bombing?

Summary

Identifying and removing email addresses submitted via list bombing requires a multi-faceted approach that combines preventative measures, detection techniques, and ongoing monitoring. Preventative measures include confirmed opt-in (COI), honeypot fields, reCAPTCHA (including v3), signup throttling, client-side Javascript validation, and blocking signups from IPs on Spamhaus's XBL. Detection techniques involve analyzing signup patterns for anomalies, auditing subscription data, monitoring bounce rates, and using bot management solutions and spam databases. Regularly updating blocklists and leveraging external services like CleanTalk and Project Honey Pot are also beneficial. Authentication and authorization methods play a key role in minimizing the number of fake signups.

Key findings

  • Confirmed Opt-In (COI): COI is a strong defense against list bombing by ensuring that only legitimate subscribers are added.
  • Honeypot Fields: Honeypot fields effectively identify and block bots by trapping them in hidden form fields.
  • reCAPTCHA & v3: reCAPTCHA, especially v3, helps to differentiate between humans and bots, reducing automated submissions.
  • Signup Throttling: Limiting the number of signups from a single IP can prevent bots from flooding the system.
  • Javascript Validation: Client-side validation can catch many obvious bot submissions before they reach the server.
  • Spamhaus XBL Blocking: Blocking signups from IPs on Spamhaus's XBL can effectively prevent botnet signups.
  • Subscription Audit Data: Analyzing subscription audit data helps identify suspicious signups and patterns.
  • Pattern Analysis: Identifying unusual signup patterns, such as high volumes or similar data, can reveal list bombing attacks.
  • Bounce Rate Monitoring: High bounce rates after a signup period indicate many invalid or fake addresses.
  • Bot Management Solutions: Bot management solutions analyze traffic to detect and block malicious bot activity.
  • Spam Databases: Checking IPs against known spam databases identifies malicious signups.
  • External Services: Services like CleanTalk and Project Honey Pot can flag suspicious activity and IPs.

Key considerations

  • Multi-Layered Approach: Employ a combination of prevention, detection, and monitoring techniques for best results.
  • Adaptability: List bombing tactics evolve, requiring continuous adaptation of strategies.
  • False Positive Management: Be cautious of false positives that block legitimate users.
  • Data Privacy Compliance: Ensure that data handling for bot detection complies with privacy regulations.
  • Authentication Methods: Employ strong authentication and authorization to reduce fake signups.
  • Resource Allocation: Allocate sufficient resources to implement and maintain anti-list bombing measures.

What email marketers say
10Marketer opinions

Identifying and removing email addresses submitted via list bombing involves a multi-faceted approach focusing on prevention, detection, and remediation. Prevention methods include implementing confirmed opt-in (COI), CAPTCHA, honeypot fields, and signup throttling. Detection strategies involve analyzing signup patterns for anomalies, monitoring bounce rates, and using client-side JavaScript validation. Additionally, leveraging external services like CleanTalk, updating blocklists, and implementing authentication measures are valuable.

Key opinions

  • Confirmed Opt-in: Implementing a confirmed opt-in process ensures that only legitimate subscribers are added to the list.
  • CAPTCHA: Using reCAPTCHA on signup forms effectively prevents automated bot submissions.
  • Honeypot Fields: Honeypot fields help identify and block bot-generated signups by detecting submissions with data in hidden fields.
  • Signup Pattern Analysis: Analyzing signup patterns reveals anomalies indicative of list bombing, such as spikes in signups from specific regions or unusual email addresses.
  • Signup Throttling: Signup throttling limits the number of signups from a single IP, preventing bots from flooding the system.
  • Client-Side Validation: Client-side JavaScript validation catches obvious bot submissions with invalid email formats.
  • External Services: Services like CleanTalk flag suspicious IPs, enhancing detection capabilities.
  • Blocklist Updates: Regularly updating blocklists prevents known spammers and bot IPs from signing up.
  • Bounce Rate Monitoring: Monitoring bounce rates detects high volumes of invalid or fake signups.

Key considerations

  • Layered Approach: A layered approach combining prevention, detection, and remediation is crucial for effective list bombing mitigation.
  • Adaptability: List bombing techniques evolve, so strategies must be continuously adapted.
  • False Positives: Carefully consider the risk of false positives when implementing aggressive blocking measures to avoid hindering legitimate users.
  • Data Privacy: Ensure compliance with data privacy regulations when collecting and analyzing user data for fraud detection.
  • Resource Allocation: Allocate sufficient resources to implement and maintain anti-list bombing measures.
Marketer view

Email marketer from Sendinblue suggests using honeypot fields on signup forms. These are hidden fields that bots often fill out, while legitimate users won't see them. Identifying submissions with data in these fields indicates a bot-generated signup.

February 2024 - Sendinblue
Marketer view

Email marketer from Email Geeks recommends to check out cleantalk which will flag IPs on their network.

February 2023 - Email Geeks
Marketer view

Email marketer from Reddit suggests analyzing signup patterns for anomalies. Look for spikes in signups from specific countries or IP ranges, or signups with unusual usernames or email addresses. This can help identify and remove bot-generated signups.

December 2023 - Reddit
Marketer view

Email marketer from StackOverflow suggests implementing client-side JavaScript validation to catch obvious bot submissions before they reach the server. This can filter out signups with invalid email formats or other suspicious data.

January 2023 - StackOverflow
Marketer view

Email marketer from Email Geeks shares that honeypot fields can also reduce bot submissions.

June 2024 - Email Geeks
Marketer view

Email marketer from Reddit recommends implementing signup throttling to limit the number of signups from a single IP address within a specific timeframe. This can help prevent bots from flooding the system with fake accounts.

December 2023 - Reddit
Marketer view

Email marketer from Email Marketing Forum recommends closely monitoring bounce rates after a signup. High bounce rates can indicate that many of the signups are invalid or fake, suggesting a list bombing attack.

May 2024 - Email Marketing Forum
Marketer view

Email marketer from Litmus explains that a good defense against list bombing is implementing a confirmed opt-in (COI) process, also known as double opt-in, which requires users to verify their email address before being added to the list. This helps ensure that only legitimate subscribers are added.

July 2021 - Litmus
Marketer view

Email marketer from MailerQ shares that implementing reCAPTCHA on signup forms can effectively prevent bots from automatically submitting large numbers of email addresses. reCAPTCHA challenges users to prove they are human, blocking automated submissions.

April 2023 - MailerQ
Marketer view

Email marketer from Email Marketing Forum suggests regularly updating your blocklists with known spammers and bot IPs. This can help prevent them from signing up in the first place.

January 2024 - Email Marketing Forum

What the experts say
8Expert opinions

Identifying and removing email addresses submitted via list bombing involves analyzing subscription data, implementing preventative measures, and utilizing external resources. Analyzing signup patterns for anomalies like similar names using hex codes, direct API submissions, or signups during specific attack windows is crucial. Implementing a hidden phone field and disallowing signups from IPs on Spamhaus's XBL are valuable tactics. While CAPTCHA helps, it's not foolproof. Authentication methods like double opt-in are essential for preventing fake signups.

Key opinions

  • Subscription Audit Data: Subscription audit data provides valuable insights for identifying and removing fraudulent signups.
  • Pattern Recognition: Identifying patterns in signup data, such as similar names using hex codes, helps detect list bombing attempts.
  • Hidden Phone Field: A hidden phone field can trap programmatic bombers, as they often fill in all fields regardless of visibility.
  • Spamhaus XBL: Disallowing signups from IPs on Spamhaus's XBL can effectively block botnet signups.
  • Signup Pattern Analysis: Monitoring signup volumes, sources, and email address patterns uncovers list bombing attempts.
  • CAPTCHA Limitations: While helpful, CAPTCHA is not a complete solution, and advanced bots can bypass it.
  • Double Opt-in Importance: Implementing double opt-in is critical for verifying subscriber consent and preventing fake signups.

Key considerations

  • Comprehensive Analysis: Combine multiple data points and analysis techniques for effective detection.
  • Evolving Tactics: List bombing techniques evolve, requiring continuous adaptation of detection and prevention strategies.
  • False Positives: Carefully balance security measures with the potential for false positives that impact legitimate users.
  • Proactive Prevention: Prioritize proactive measures like double opt-in to minimize the risk of list bombing from the outset.
Expert view

Expert from Email Geeks shares that they disallow signups from IPs on Spamhaus's XBL (but not PBL!) as it seems to be a good indicator of whether or not a signup IP is part of a botnet.

July 2021 - Email Geeks
Expert view

Expert from Email Geeks explains that your own subscription audit data is your best bet for removal after the fact.

December 2022 - Email Geeks
Expert view

Expert from Word to the Wise recommends implementing authentication and authorization methods, such as double opt-in, to reduce the number of fake signups making it onto your lists in the first place. Making sure the subscriber has actually consented to receiving messages from you is important for all kinds of deliverability reasons.

February 2025 - Word to the Wise
Expert view

Expert from SpamResource explains that one method to identify list bombing is to watch for unusual signup patterns. This includes looking for high volumes of signups from similar IP ranges, using disposable email addresses, or providing nonsensical names.

October 2023 - SpamResource
Expert view

Expert from Email Geeks shares that you can sometimes see patterns in the data itself related to list bombing, such as similar names using Hex Codes, addresses submitted directly to back-end APIs, or addresses added within specific time frames during the attack.

November 2024 - Email Geeks
Expert view

Expert from Email Geeks explains to look at all signups over the period of concern. Check if the same email signed up to multiple lists, if multiple signups came from the same IP, and look for anything distinctive in the user-agent or the data POSTed.

September 2021 - Email Geeks
Expert view

Expert from SpamResource shares that implementing CAPTCHA can prevent many automated bot submissions, but it's not foolproof. Advanced bots can sometimes bypass CAPTCHAs, so it's important to use other layers of protection as well.

August 2022 - SpamResource
Expert view

Expert from Email Geeks shares that another tactic is a `phone` field that's hidden. Most (but not all) programmatic bombers won't recognize it as hidden and provide a submission. Then any record where that's got a value is suspect.

December 2024 - Email Geeks

What the documentation says
5Technical articles

Identifying and removing email addresses submitted via list bombing can be achieved through a combination of strategies and tools. Bot management solutions, spam databases, and Project Honey Pot can help detect and block malicious activity. Implementing CAPTCHA, rate limiting, and input validation also help in preventing automated attacks. reCAPTCHA v3 offers a user-friendly approach to identify suspicious behavior based on risk scores.

Key findings

  • Bot Management: Bot management solutions analyze traffic patterns to identify and mitigate automated attacks such as list bombing.
  • Spam Databases: Checking IP addresses against spam databases helps identify malicious signups associated with spam activity.
  • Project Honey Pot: Project Honey Pot's system can detect spammers and prevent them from obtaining email addresses, reducing the risk of list bombing.
  • Form Protection: CAPTCHA, rate limiting, and input validation are essential measures for preventing automated attacks on web forms.
  • reCAPTCHA v3: reCAPTCHA v3 uses a risk score to identify suspicious behavior without requiring user interaction, providing a seamless user experience.

Key considerations

  • Comprehensive Approach: Employing a combination of different tools and techniques is more effective than relying on a single solution.
  • Accuracy: Balance the need for security with the potential for false positives, ensuring that legitimate users are not blocked.
  • Maintenance: Regularly update and maintain bot management solutions, spam databases, and CAPTCHA implementations to adapt to evolving bot tactics.
  • User Experience: Consider the impact on user experience when implementing security measures, and choose solutions that minimize disruption for legitimate users.
Technical article

Documentation from OWASP explains that using techniques like CAPTCHA, rate limiting, and input validation are key measures for preventing automated attacks and list bombing on web forms.

July 2024 - OWASP
Technical article

Documentation from Google explains how to implement reCAPTCHA v3, which uses a risk score to identify suspicious behavior without requiring user interaction. This can help prevent bots from signing up without disrupting the user experience.

August 2024 - Google
Technical article

Documentation from Project Honey Pot explains that using their system and tracking can help to detect spammers and stop them from obtaining email addresses from your website, which can lead to list bombing.

August 2022 - Project Honey Pot
Technical article

Documentation from Cloudflare explains that using a bot management solution can help identify and mitigate automated attacks like list bombing. Bot management tools analyze traffic patterns to detect and block malicious bot activity.

November 2021 - Cloudflare
Technical article

Documentation from Stop Forum Spam shares that checking IP addresses against known spam databases can help identify malicious signups. If an IP address is associated with spam activity, the signup can be blocked.

December 2023 - Stop Forum Spam