What are common false invalid results?

False invalids are legitimate addresses incorrectly flagged for removal. Common causes: catch-all domains that can't confirm individual addresses, temporary server issues during validation, anti-validation measures blocking checks, and overly aggressive risk scoring.

Specific scenarios: corporate servers blocking external validation, privacy-focused services refusing to confirm addresses, international domains with unusual configurations, and recently created addresses not yet in databases.

Mitigate by: cross-referencing with engagement data (engaged addresses are real), implementing soft rather than hard removal for uncertain results, testing validation accuracy against known-good addresses, and preserving addresses with any positive engagement signals.