Emails tied to domains known for spam or fraudulent activity.

Sometimes referred to as abuse prone emails, these emails are tied to high-frequency spam complaints often with malicious intent.

Addresses pointing to non-existent mailbox.

Addresses which have returned a permanent delivery failures preventing email delivery.

Email addresses flagged as restricted for sending email to.

Catches emails sent to a domain where a mailbox does not exist.

Domains without valid mail server configurations.

IPs unable to deliver messages to the recipient's server.

Single use address, often for discounts or bypassing account creation restrictions. Ineffective for long-term marketing.