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Glossary

What Is Email Poisoning? (And How to Detect It)

Email poisoning is a deliberate tactic to ruin your sender reputation and cause deliverability issues. Learn what it is, how it works, and how to defend against it.

Lero Team
4 min read
12/19/2024

What is email poisoning?

Email poisoning is a malicious tactic where someone intentionally submits fake or invalid email addresses into your forms, lead magnets, or opt-in lists to harm your deliverability.

It's also known as:

  • List poisoning
  • Lead form spamming

🤔Why do people use email poisoning?

Email poisoning is used to:

  • Crash autoresponders by flooding them with fake signups
  • Damage your sender reputation with high bounce/spam rates
  • Trick you into sending to honeypots or spam traps
  • Waste your time and money with bad leads

It's often automated with bots or scripts targeting open forms.

🔍How do I know if I've been poisoned?

Warning signs include:

  • Sudden spike in bounces or fake-looking domains
  • Huge increase in signups from suspicious IPs or countries
  • Emails that fail validation (e.g. asdf123@zzzz.com)
  • Increased complaints, unsubscribes, or blacklist hits

🛡️How can I prevent email poisoning?

Protect your forms with:

✅ Email validation

(like Lero)

✅ CAPTCHA

or reCAPTCHA

✅ Rate limiting

per IP

✅ Double opt-in

confirmation

✅ Monitor

and block known bot IPs

📌 Summary

Email poisoning is a malicious tactic where fake or invalid email addresses are intentionally submitted into your forms to damage your sender reputation and deliverability. Don't wait until it hits—validate before you send.

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