What makes an email address "toxic" or risky?

A toxic address is any address that threatens your deliverability or reputation. These include pristine spamtraps, which are created solely to catch scrapers, recycled spamtraps, which are abandoned inboxes reactivated by providers, abuse prone inboxes, bot generated entries, parked domains, dead domains, and role accounts that frequently mark messages as spam. Toxic addresses behave like unstable cargo that can contaminate the entire shipment. Even a small amount can sink performance.