Pre-campaign verification is critical since May 2025 when Google and Yahoo started enforcing hard limits: bounces under 2%, spam complaints under 0.3%. Exceeding either gets you throttled or blocked.
Layer your verification:
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Primary verification - Run your list through a dedicated verifier. ZeroBounce achieves 96-98% accuracy in independent tests (not the 99.6% they claim). NeverBounce is more conservative - fewer emails marked as safe, but virtually no bounces.
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Catch-all handling - This is where most teams get burned. Catch-all domains can make up 50% of lead lists. Options: exclude catch-alls entirely (safest), or add a second-pass verifier like BounceBan which caught 62 additional bad addresses on a 483-lead list after ZeroBounce.
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Name-email matching - Verify the email belongs to the right person, not just that it's deliverable. Waterfall enrichment can stop on the first "valid" email even if it's wrong for that person.
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Recency check - If your list is older than 30 days, re-verify. Job changes happen constantly and enrichment data can be 2-3 weeks behind reality.
Budget option: MillionVerifier refunds credits for unknown and catch-all results, making it cost-effective for large lists where you expect high catch-all rates.