Greylisting: What It Is and How It Affects Verification

Greylisting temporarily rejects emails to filter spam. Legitimate senders retry; spammers often don't.

How It Works

1. New sender is temporarily rejected (4xx error)
2. Legitimate mail servers retry after delay
3. After retry, sender is whitelisted
4. Spammers often don't retry

Impact on Verification

Greylisting can cause false "undeliverable" results in email verification if the verifier doesn't retry.

Conclusion

Good verification services handle greylisting with retry logic. MailVeri does this automatically.