Why do “verified” B2B email lists still have such poor deliverability?

I’ve run into this problem repeatedly while doing B2B outreach and I’m curious how others here see it.

Even when buying lists marketed as verified or cleaned, deliverability is often terrible: bounces, catch-alls, or emails that were valid months ago but are dead now.

From your experience, what’s usually the real issue?

• Data being outdated too quickly?

• Weak or one-time verification?

• Catch-all domains passing basic checks?

• Sellers optimizing for volume over accuracy?

I’m especially interested in what actually worked for you in practice — whether that’s rechecking policies, filtering strategies, or changes in how you source leads.

Would love to hear real-world approaches, not theory.