Preventing spam subscriptions and subscription bombing requires a multifaceted approach involving both technical implementations and strategic monitoring. Experts suggest checking signup metadata, implementing CAPTCHA, honeypots, confirmed opt-in (COI), and rate limiting. Additionally, blocking disposable email addresses, email address validation, cleaning inactive subscribers from the list, and monitoring signup sources are essential. Masking email addresses on websites to prevent harvesting is also recommended. However, some caution against blocking '+' addresses, as they can be legitimate, and emphasize that double opt-in (DOI), while generally helpful, can be exploited if other measures are lacking. A holistic approach involving multiple layers of defense is most effective.
13 marketer opinions
Preventing spam email subscriptions and subscription bombing involves a multi-faceted approach. Key strategies include implementing honeypots, CAPTCHA, and double/confirmed opt-in processes to filter out bots and ensure genuine subscriber interest. Maintaining a clean email list by removing inactive subscribers is crucial, as is email address validation. Blocking disposable email addresses and monitoring signup sources are also recommended. It's crucial to note that double opt-in can be part of the problem if not implemented correctly. Some advise against blocking email addresses with '+', as they are legitimately used by some to tag their email addresses.
Marketer view
Email marketer from Email Geeks warns that double opt-in (DOI) can become part of a spam bomb if other preventative measures aren't in place.
23 Nov 2021 - Email Geeks
Marketer view
Email marketer from StackOverflow suggests implementing strict email address validation to filter out invalid or suspicious email addresses during the subscription process.
20 Oct 2023 - StackOverflow
5 expert opinions
To prevent spam email subscriptions and subscription bombing, experts suggest checking signup metadata (IP, user-agent) for suspicious activity and implementing measures like CAPTCHA and confirmed opt-in (COI). Masking email addresses on websites helps prevent address harvesting. Removing inactive subscribers is vital for maintaining good deliverability and avoiding spam flags.
Expert view
Expert from Email Geeks suggests captcha and confirmed opt-in (COI) as strong measures against subscription bombing.
2 Aug 2024 - Email Geeks
Expert view
Expert from Word to the Wise stresses the importance of confirmed opt-in (COI) to ensure subscribers genuinely want to receive emails, filtering out bot signups.
16 Jun 2022 - Word to the Wise
4 technical articles
Preventing spam subscriptions and subscription bombing involves several technical methods. reCAPTCHA v3 verifies interactions based on a score, identifying bots without user friction. Honeypots, decoy form fields, attract and identify malicious bots. Rate limiting restricts sign-up attempts from a single IP address within a timeframe. Databases of known spam IPs and emails, like StopForumSpam, can block malicious sign-ups.
Technical article
Documentation from OWASP explains that honeypots can be created as decoy form fields that are invisible to users but will be filled out by bots, thereby identifying them as malicious.
23 Nov 2024 - OWASP
Technical article
Documentation from Google Developers explains that implementing reCAPTCHA v3 helps to verify if an interaction is legitimate without user friction, using a score-based system to detect bots.
16 Jan 2024 - Google Developers
How can I ensure deliverability when many signups are from qq.com addresses and what steps can I take to prevent spam signups?
How can I identify and prevent spam/bot traffic at email subscription points?
How can I identify and prevent suspicious or bot-generated email addresses in my lists?
How can I identify and remove email addresses submitted via list bombing?
How can I prevent bots from signing up for my newsletter and marking it as spam?
How should I handle Abuse Feedback Reports from USGOabuse.net regarding subscription bombing?