Start with NeverBounce's own wording. The guarantee lives at neverbounce.com/help/our-guarantee, and a separate help article covers quality reviews. Read both in a browser before you rely on them, and save a copy with the date, because help-centre terms change without a version number. The NeverBounce review covers the rest of its offer.
Here's how the other published guarantees were built on 24 September 2026. Emailable promises no more than 1% bounces on addresses it marks deliverable, with a full refund on qualifying addresses, if you send to at least 1,000 of them within 24 hours from an opt-in source and claim within 72 hours. DeBounce guarantees a 97.5% deliverability rate and pays three times the credits for every 1% shortfall. Kickbox offers a 95% deliverability guarantee on addresses downloaded as deliverable.
The pattern is the same everywhere. A guarantee covers only the addresses marked valid or deliverable, so catch-all and unknown rows sit outside it. It needs a real send within a tight window, often 24 to 48 hours, and usually from an opt-in list. And the remedy is credits or a refund of what those rows cost.
That's why a guarantee and an accuracy claim answer different questions. An accuracy figure counts only the addresses that got a definite verdict. A guarantee caps bounces on the ones marked good. Neither tells you how much of your list got a verdict at all. Our post on the 99% accuracy problem shows how the denominator shapes the headline.
ZapBounce puts that missing number on every report. You see coverage, the share of your list that reached a verdict, next to accuracy. Every row carries the mail server's smtp_code and a billed flag, so you can audit each result yourself. unknown results and duplicates are never billed, and checks cost $5 for 1,000. How it works walks through the check.
Related questions
Where can I read the NeverBounce guarantee?
NeverBounce publishes it in its help centre at neverbounce.com/help/our-guarantee. Read it in a browser and save a dated copy, since help articles change without notice.
Do email verifier guarantees cover catch-all addresses?
The guarantees read on 24 September 2026 covered addresses marked deliverable or valid. Catch-all and unknown rows fell outside them. Check the exact wording for any vendor you use.
What does a deliverability guarantee usually pay out?
Most pay in credits or refund what the qualifying addresses cost. DeBounce, for example, paid three times the credits for every 1% below its 97.5% target on 24 September 2026.
How does ZapBounce show that its results hold up?
ZapBounce reports coverage beside accuracy, and every row carries the mail server's smtp_code and a billed flag. You can audit any result yourself, and unknown results are never billed.