What backend validations can be implemented for email opt-in and account registration to prevent spam?

Email marketer from Marketing Community shares that implement progressive profiling, where you request additional information from users over time rather than all at once during registration, can help deter spammers who prefer to provide minimal information.

Marketer from Email Geeks suggests that a honeypot, along with reCAPTCHA and double opt-in, can address signup form abuse. They also mention that poor practices, like requiring an address unnecessarily, can lead to spam traps.

Email marketer from Online Forum shares that a Email Verification API performs deep email checks by connecting to the mail server to determine the email’s deliverability.

Email marketer from Email Security Blog explains that phone number verification (SMS verification) adds an additional layer of security by ensuring that the user has access to a valid phone number, discouraging spammers who often use fake or temporary numbers.

Email marketer from Tech Blog mentions using third-party email verification services to validate the email address's syntax, domain, and mailbox existence in real-time, ensuring that only valid email addresses are accepted.

Email marketer from Security Blog explains employing CAPTCHA alternatives, such as behavioral analysis or challenge-response tests, to differentiate between humans and bots without relying solely on traditional CAPTCHAs that can be bypassed by advanced bots.

Email marketer from Webmaster Forum shares that adding a hidden "honeypot" field to the registration form, which is invisible to human users but can be filled by bots, helps identify and block spam submissions.

Email marketer from Online Forum explains that limiting the number of accounts that can be created from a single IP address within a certain time frame can help prevent automated account creation by bots.

Marketer from Email Geeks explains how to build a honeypot by using an invisible field on the form. Submissions with a value in this field are discarded, as humans won't fill it out. They shared some repos that may help build something.

Email marketer from Stack Overflow explains that email validation can be achieved by checking the format, verifying the domain exists, and sending a confirmation email to ensure the address is valid.

Email marketer from Reddit explains that using a disposable email address (DEA) detection service or maintaining a DEA domain blocklist can prevent registrations from temporary or throwaway email addresses often used by spammers.

Marketer from Email Geeks mentions that Kickbox & co provide APIs to check domains and addresses.

Email marketer from Quora shares that checking the IP address of the user against known spam blacklists or reputation databases can help identify and block registrations from suspicious or malicious IP addresses.

Expert from Spam Resource explains that Shared IPs can be problematic and lead to reputation issues affecting deliverability. They also recommend monitoring IP reputation and avoiding association with known spammers.

Expert from Word to the Wise shares that Rate limiting signups, especially when combined with additional data collection, helps prevent bots from targeting specific addresses and creating list bombing attacks.

Expert from Word to the Wise explains that using confirmation opt-in helps to remove users who don't want to subscribe to emails.

Documentation from OWASP shares that implementing rate limiting on account registration endpoints can prevent bots from creating multiple spam accounts within a short period.

Documentation from Project Honey Pot explains that using a Project Honey Pot to setup traps can identify spammers and those engaged in unsolicited email harvesting, and block registration from users.

Documentation from Google Developers explains that reCAPTCHA can be implemented to distinguish between human users and bots during form submissions, preventing automated spam registrations.

Documentation from IETF explains that implementing SPF (Sender Policy Framework) records helps prevent email spoofing by verifying that emails are sent from authorized mail servers, reducing the likelihood of spam.