How can I identify and prevent suspicious or bot-generated email addresses in my lists?
Michael Ko
Co-founder & CEO, Suped
Published 16 Apr 2025
Updated 19 Aug 2025
7 min read
Maintaining a clean and legitimate email list is crucial for effective email marketing and safeguarding your sender reputation. Lately, I've seen an increase in suspicious or bot-generated email addresses creeping into various lists, and it's a concern for many. These aren't just harmless additions, they can severely impact your deliverability, leading to higher bounce rates and potentially landing your domain on a blocklist (or blacklist).
Identifying these addresses can be tricky, as they sometimes mimic legitimate patterns, while other times they appear as random strings of characters. The challenge lies in distinguishing between a genuine, if unusual, signup and automated bot activity.
I'll walk you through how to pinpoint these unwanted entries and, more importantly, put robust measures in place to prevent them from infiltrating your lists in the first place. Protecting your list isn't a one-time task, it's an ongoing process vital for long-term email success.
Identifying suspicious patterns
Suspicious email addresses often exhibit distinct characteristics that set them apart from genuine sign-ups. One common indicator is a gibberish username combined with what appears to be a corporate or legitimate domain. For instance, an address like bcevy.debaebyy@preferredmutual.com may seem odd but the domain is real, suggesting either a privacy feature or a bot trying to blend in. It's also worth checking if the character count before and after the '.' matches actual addresses from that domain, which could hint at an obfuscation technique.
Another red flag is the source of the traffic. If suspicious addresses are coming from unusual IP addresses, such as those associated with VPNs, Tor exit nodes, or known botnets, it’s a strong indication of automated activity. While some VPNs may publish their exit points, many do not, making it harder to track. You should investigate if these sign-ups originate from the same few IPs or a wide, disparate range.
Beyond sign-ups, bot activity can also appear as suspicious clicks in your email campaigns. If your tracking shows clicks from addresses not in your database, especially with random username formats, it could indicate corporate security systems or email scanning tools that automatically click links. This type of activity, while not directly adding to your list, can skew your engagement metrics and make it harder to assess true subscriber interest.
Prevention at the source: signup forms
The most effective way to prevent bot-generated addresses from corrupting your lists is to implement robust validation at the point of signup. One of the simplest yet most effective measures is double opt-in (COI). This requires users to confirm their subscription via an email link, effectively weeding out invalid or bot-submitted addresses. While double opt-in does not stop the initial signup attempt, it prevents the unconfirmed addresses from receiving your emails, thereby protecting your sender reputation from bounces and complaints.
Beyond double opt-in, integrating CAPTCHA challenges, such as Google reCAPTCHA v3, into your signup forms can significantly reduce bot submissions. This fraud detection tool assesses user behavior to distinguish between human and bot interactions. You can also deploy honeypot fields, which are hidden form fields that only bots will attempt to fill, allowing you to flag and block these submissions silently.
I often recommend using a combination of these methods for the best defense. For example, alongside double opt-in and CAPTCHA, consider implementing an email verification service at the point of signup. These services can identify and reject disposable or high-risk email domains in real-time, preventing them from ever entering your list. You can explore a complete guide on how to protect your website from spam bots for more detailed tactics.
Double opt-in
Verification: Requires subscribers to confirm their email address, ensuring validity.
Quality: Builds a cleaner list with engaged subscribers, reducing bounces.
Deliverability: Improves sender reputation and inbox placement.
List hygiene and maintenance
Even with strong preventative measures, some suspicious addresses might still slip through. Regularly cleaning your email list is a non-negotiable step to maintain good deliverability and protect your sender reputation. This involves identifying and removing invalid, inactive, or bot-generated addresses.
A key aspect of list hygiene is monitoring your bounce rates. A sudden spike in hard bounces often indicates that fake email addresses or spam traps have infiltrated your list. Spam traps are email addresses used by internet service providers (ISPs) and anti-spam organizations to identify senders of unsolicited email. Hitting these can quickly lead to your IP or domain being added to a blocklist.
Regularly using an email verification service is another powerful tool. These services can scrub your existing list, identifying and flagging potentially harmful addresses that might be spam traps, disposable emails, or simply invalid. Think of it as a proactive defense that keeps your list healthy and reduces the risk of deliverability issues. For a deep dive into this, you can refer to a complete guide to email list cleaning.
Impact on deliverability and sender reputation
The impact of suspicious and bot-generated email addresses extends beyond just inflating your list numbers. They can significantly harm your sender reputation, leading to poor inbox placement, increased spam complaints, and even blocklisting. When email providers see a high volume of emails sent to invalid or unengaged addresses, they flag your sending domain as potentially suspicious.
This is where DMARC monitoring becomes critical. DMARC reports provide valuable insights into your email authentication results, but they can also highlight unusual patterns like unexpected forwarding or large volumes of unauthenticated mail, which might be indicative of list bombing or bot activity. By analyzing these reports, you can pinpoint specific issues and take corrective action.
It’s important to remember that dealing with bot traffic is an ongoing battle. Spammers and bots constantly evolve their tactics, so staying vigilant and adapting your defense mechanisms is key. Regularly reviewing your sign-up sources, bounce rates, and engagement metrics will help you stay ahead.
The risk of bot-generated email addresses
Spam traps: Sending to these can severely damage your sender reputation.
Blocklisting: High bounce rates and complaints can lead to placement on email blocklists (blacklists).
Skewed data: Bot clicks and sign-ups distort your analytics, making accurate campaign assessment difficult.
Ensuring a healthy email list
Staying on top of bot-generated email addresses is fundamental for maintaining a healthy email ecosystem. By implementing proactive measures at signup, regularly cleaning your lists, and continuously monitoring your email performance, you can protect your sender reputation and ensure your legitimate messages reach their intended recipients. It’s a commitment to email hygiene that pays dividends in deliverability and engagement.
Remember, the goal is not just to remove bad addresses, but to prevent them from entering your system in the first place. This layered approach creates a more resilient email program and frees up your resources to focus on genuine subscriber engagement, rather than fighting unwanted traffic.
By following these strategies, you can significantly reduce the threat of suspicious and bot-generated emails, ensuring your email marketing efforts remain effective and your sender reputation stays strong.
Views from the trenches
Best practices
Implement double opt-in on all signup forms to verify email addresses.
Use CAPTCHA (especially reCAPTCHA v3) to detect and block automated submissions.
Regularly validate your email lists using a reputable verification service.
Monitor IP addresses of signups for patterns indicating bot activity, like Tor or VPN usage.
Analyze DMARC reports for suspicious click patterns from corporate security systems.
Common pitfalls
Not using double opt-in, leading to unverified email addresses on lists.
Disabling CAPTCHA or other bot protection measures without re-enabling them.
Failing to regularly clean email lists, accumulating invalid addresses and spam traps.
Ignoring high bounce rates, which signal the presence of suspicious emails.
Misinterpreting bot clicks as genuine engagement, skewing analytics.
Expert tips
Consider using honeypot fields in your forms to silently catch bot submissions.
Look for gibberish usernames on legitimate-looking domains as a common bot indicator.
Investigate complaint rates to identify potential list bombing or malicious sign-ups.
Be aware that corporate security systems might generate clicks from random addresses.
Utilize an email address validation tool to identify high-risk domains.
Marketer view
A marketer from Email Geeks says they saw gibberish email addresses with corporate domains in their click tracking, but these were not in their database, suggesting bot clicks.
2023-02-08 - Email Geeks
Expert view
An expert from Email Geeks says it's unlikely to be an Apple Hide My Email feature if the domain is corporate, and suggested looking at connecting IP addresses for signs of Tor or VPN usage.
Google reCAPTCHA v3, into your signup forms can significantly reduce bot submissions. This fraud detection tool assesses user behavior to distinguish between human and bot interactions. You can also deploy honeypot fields, which are hidden form fields that only bots will attempt to fill, allowing you to flag and block these submissions silently.
