Combating spam and bot traffic at email subscription points requires a layered approach. Standard practices like CAPTCHA and double opt-in are foundational, but increasingly sophisticated bots necessitate advanced techniques. These include capturing signup audit trails, using tiered CAPTCHAs, implementing honeypot fields (hidden forms), performing reverse DNS lookups, and analyzing signup behavior for suspicious patterns. Server-side validation (using PHP) is crucial as bots often bypass client-side JavaScript. Rate limiting, bot management tools (like Cloudflare), and blocking known spam IPs/countries provide additional layers of defense. Integrating with services like Project HoneyPot and maintaining strong transactional relationships are also beneficial. However, the effectiveness of CAPTCHA is diminishing due to captcha farms, and reliance on ESPs for subscription checks is essential, requiring proactive communication with their abuse desks.
14 marketer opinions
To combat spam and bot traffic at email subscription points, marketers employ various techniques. Standard practices include CAPTCHA and double opt-in, with some suggesting hidden form fields (honeypots) in the HTML to deter automated sign-ups. Analyzing signup behavior, such as location, time, and referrer, can flag suspicious activity. While Mailchimp supports hidden fields, some advocate for server-side PHP solutions to validate forms. Restricting role-based accounts (abuse@, postmaster@) is also recommended. CAPTCHA's effectiveness is questioned due to captcha farms. Utilizing IP address blocking, JavaScript validation, analyzing form completion time, and blocking specific countries add further layers of defense.
Marketer view
Marketer from Email Geeks suggests that depending on scale, one can run analytics based on typical sign-up behaviour to flag suspicious behaviours for manual inspection, using data-points like location, time, referrer, etc.
25 Oct 2023 - Email Geeks
Marketer view
Email marketer from Reddit suggests analysing the time it takes a user to fill out the form, and identify if it is quicker than a human could reasonably do so.
21 Sep 2023 - Reddit
7 expert opinions
Experts recommend a multi-faceted approach to identifying and preventing spam and bot traffic during email subscription. Capturing a detailed audit trail (timestamp, IP, browser data), employing tiered CAPTCHAs, and performing reverse DNS lookups are crucial. Hidden form fields act as traps, particularly with JavaScript. Server-side ESP checks are necessary as many bots bypass client-side validation. A strong transactional relationship is important. Consulting with the ESP's abuse desk is advised before involving the development team.
Expert view
Expert from SpamResource suggests performing reverse DNS lookups on the IP addresses of subscribers. If the IP address doesn't have a valid reverse DNS record, or if it resolves to a dynamic hostname, it could be a sign of a bot or spammer.
14 Jan 2024 - SpamResource
Expert view
Expert from Email Geeks states that ESPs that can't handle subscription checks are a problem, and that subscription checks need to be server side, as most dumber bots aren't handling JS.
2 Jun 2024 - Email Geeks
4 technical articles
Technical documentation emphasizes using advanced tools and techniques to identify and prevent bot traffic at email subscription points. Google reCAPTCHA employs risk analysis, OWASP recommends rate limiting, Cloudflare advocates bot management tools, and Project HoneyPot offers a distributed system for identifying malicious networks.
Technical article
Documentation from Project HoneyPot provides a distributed system for identifying malicious bot networks, you can use a tool like this to identify networks of bots signing up.
12 Mar 2022 - Project HoneyPot
Technical article
Documentation from OWASP explains that implementing rate limiting on signup forms restricts the number of requests from a single IP address within a specific timeframe, preventing bots from flooding the system with spam subscriptions.
25 Jul 2021 - OWASP
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