How can I prevent non-human interaction (NHI) during email signup and confirmation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 17 Aug 2025
7 min read
Dealing with non-human interaction (NHI) during email signup and confirmation has become a significant challenge for anyone managing email lists. These automated systems, often bots or security scanners, can inflate your metrics, skew your data, and even negatively impact your sender reputation. While completely eliminating NHI might be an unrealistic goal, implementing robust strategies can significantly mitigate its effects.
The primary concern with NHI, especially at the point of signup or during the confirmation process, is that it contaminates your audience data. If a significant portion of your new signups aren't real humans, your engagement rates will suffer, leading to lower inbox placement over time. This can cause legitimate emails to land in the spam folder, frustrating your genuine subscribers.
In this guide, I'll walk you through practical steps and technical implementations to reduce NHI and ensure your email list comprises engaged, human subscribers. From initial form submission to the final confirmation click, we'll explore methods to safeguard your email program against automated interference and maintain a healthy, deliverable list.
Initial signup form protection
The first line of defense against non-human interaction begins at your signup forms. Implementing basic yet effective measures can deter a large percentage of automated signups before they even hit your system. These methods focus on identifying and blocking suspicious activity early on, protecting your email list from contamination.
One of the most effective methods is a properly configured CAPTCHA or reCAPTCHA on your forms. This simple challenge can filter out many automated scripts that lack the ability to solve visual or auditory puzzles. While not foolproof, it's a critical initial barrier. Another common technique is to use honeypot fields. These are invisible fields on your form that only bots will attempt to fill. If a hidden field is populated, you know it's a bot and can immediately discard the submission without a human ever noticing. This is a subtle yet powerful method to prevent spam bot sign-ups.
Beyond visual challenges, implementing real-time email validation at the point of entry is essential. This can verify the syntax, domain existence, and even identify disposable email addresses, preventing them from entering your system. This helps to prevent disposable email signups. Rate limiting signup attempts from a single IP address can also be effective, blocking bots that try to submit numerous forms in a short period. Finally, integrating IP blocklist (or blacklist) checks, such as those provided by Spamhaus, can prevent signups from known malicious IPs. Understanding how email blacklists actually work is important here.
Confirming human intent
Once a user submits the signup form, the next critical stage for preventing NHI is the confirmation email, often part of a double opt-in process. This step is vital because it requires interaction with an actual email client and, ideally, a human user.
Double opt-in is considered a best practice for preventing fake email registrations and list bombing. It requires the subscriber to click a confirmation link within the email they receive. To enhance this, ensure that the landing page for the confirmation link requires JavaScript to be enabled. Bots or automated systems might click the link but often won't execute JavaScript, providing another layer of verification. Consider adding a soft bot check on this landing page as well, which can be a simple hidden field or a client-side behavioral analysis.
For even stronger verification, especially for high-value signups, you might consider incorporating a multi-factor authentication (MFA) code within the confirmation email. The user would then need to enter this code on the confirmation landing page, effectively transforming the process into a multi-step human interaction. While this adds friction, it greatly reduces the likelihood of NHI completing the signup process. It's about balancing user experience with the need to protect email list signup forms from bots.
Understanding and adapting to NHI
Prevention techniques
Double opt-in: Require email confirmation to verify human intent, reducing fake signups.
CAPTCHA/reCAPTCHA: Implement visual or interactive challenges on forms.
Honeypot fields: Add hidden fields that only bots will fill, flagging them automatically.
Email validation: Use real-time validation to check email syntax and domain validity.
IP blocklists: Cross-reference signup IPs against known spam sources.
JavaScript requirement: Ensure critical parts of the confirmation process require JavaScript.
While the focus is often on preventing bots, some NHI comes from legitimate security scans and privacy protection services. For example, Apple Private Relay can route traffic through various CDNs, making it difficult to differentiate from malicious bots. Attempting to block such services could inadvertently prevent real users from confirming their subscriptions or interacting with your emails.
Recognizing that some NHI is unavoidable is a key mindset shift. The goal isn't necessarily 100% elimination, but rather effective mitigation and accurate measurement. You should monitor your email engagement metrics closely, looking for anomalies that might indicate significant NHI. Keep in mind that non-human interactions can skew your data, making your open and click rates appear higher than they are for human engagement. Adjust your analysis accordingly to get a true picture of your audience's behavior. Learning about how bot signups impact email deliverability is critical.
Continuously reviewing and refining your anti-NHI measures is important. Threat actors and bot technologies evolve, so your defenses must adapt. This proactive approach helps maintain the integrity of your email list and ensures that your deliverability efforts are focused on reaching genuine human subscribers.
Impact of NHI on email deliverability
Before mitigation
Without proper defenses, you're likely to see inflated subscriber counts and engagement metrics. Your email bounce rates might increase, and your messages could start landing in spam folders for legitimate users, impacting your overall domain reputation.
Spambots can also trigger spam traps, leading to your IP or domain being added to a blocklist (or blacklist). This directly affects your email deliverability, as internet service providers (ISPs) will view your sending practices as suspicious. It also makes your email marketing efforts less efficient.
After mitigation
Implementing NHI prevention improves the quality of your email list, ensuring that your engagement metrics reflect real human interest. This leads to higher inbox placement rates and better returns on your email marketing investments. Your sender reputation remains strong, helping your emails reach their intended audience.
By actively combatting non-human signups, you reduce the risk of falling into spam traps and being placed on a blocklist. This proactive approach helps maintain clean data, allowing you to focus on genuine subscriber engagement and improve overall email deliverability. Ultimately, you are ensuring your messages are getting to the inbox.
Implementing a combination of these strategies will create a multi-layered defense against non-human interaction. No single solution is perfect, but a layered approach provides the best chance of maintaining a clean and engaged email list. Continuously monitor your list health and adjust your tactics as needed to stay ahead of evolving threats.
Remember that the goal is to optimize for human interaction. While some NHI, like security scanners, are benign, excessive bot activity can severely damage your sender reputation and deliverability. By focusing on authentic engagement, you'll see better results from your email marketing efforts. It's about ensuring that your messages get to the inbox.
Views from the trenches
Best practices
Implement double opt-in for all new email signups to verify genuine human intent.
Utilize CAPTCHA or reCAPTCHA on signup forms to filter out automated bot submissions.
Employ honeypot fields in your forms to catch and block bots discreetly.
Perform real-time email validation to check for valid syntax, active domains, and disposable addresses.
Common pitfalls
Expecting to eliminate 100% of all non-human interaction, which is unrealistic due to legitimate services like privacy relays.
Aggressively blocking IP ranges that might include legitimate privacy protection services (e.g., Apple Private Relay).
Not regularly updating bot detection methods, allowing new bot techniques to bypass existing defenses.
Relying solely on email clicks for confirmation without additional verification steps, such as MFA or JavaScript checks.
Expert tips
Continuously analyze your email engagement metrics for patterns that suggest high NHI rates.
Differentiate between malicious bot activity and benign security scans or privacy protection services.
Consider adding a soft bot check on confirmation landing pages for an extra layer of defense.
For critical sign-ups, explore implementing multi-factor authentication (MFA) within the confirmation process.
Expert view
Expert from Email Geeks says declining signups from IPs listed on Spamhaus blocklists is an effective method to stop bot sign-up attempts.
2024-03-10 - Email Geeks
Expert view
Expert from Email Geeks says verifying email addresses using a third-party service adds an additional layer of protection against invalid sign-ups.
2024-03-15 - Email Geeks
Protecting your email list integrity
Effectively preventing non-human interaction during email signup and confirmation is an ongoing process that requires a multi-faceted approach. By combining robust form protection with stringent confirmation processes, you can significantly improve the quality of your email list and safeguard your sender reputation.
While it's impossible to eliminate all NHI, the strategies discussed, from CAPTCHAs and honeypots to JavaScript requirements and email validation, provide a solid defense. Continuously monitor your email list health and adapt your methods as new threats emerge to ensure your email program remains effective and delivers messages to a genuinely engaged human audience.
Apple Private Relay can route traffic through various CDNs, making it difficult to differentiate from malicious bots. Attempting to block such services could inadvertently prevent real users from confirming their subscriptions or interacting with your emails.
