What email verification accuracy is actually achievable?

Consider two claims that are both true at once. ZeroBounce publishes 99.6%, Clearout 99.73% and Reoon over 99%. Hunter tested 15 verifiers on 3,000 real business addresses in November 2025 and found overall accuracy between 31.2% and 70.0%, with the top ten between 57.6% and 70.0%. Nobody is lying. The two numbers measure different things.

The vendor number answers a narrow question: of the addresses we returned a firm verdict on, how many were right. Strip out every address the engine declined to judge, and what remains is the easy portion. A verifier could reach 100% on that measure by answering only the questions it found simple.

Hunter's number answers the question you're actually asking: of the addresses I gave you, how many did you get right? On that denominator the unknowns count, the catch-alls count, and the score falls to something that describes the whole job.

So you need two numbers, and neither works alone. Coverage is the share of a list that got a firm verdict. Accuracy is how often those verdicts were right, with the false-positive rate stated apart, because a wrong valid costs a bounce and a wrong invalid costs a customer. Our accuracy page sets out the method, and the two numbers every verifier hides explains why the pair matters.

When you next read an accuracy claim, ask what it was divided by. If the page doesn't say, the number is decoration. Ask too what the test list held. A file of consumer Gmail addresses is a far easier exam than a business list where about 28% of the addresses sit on catch-all domains, the share one 10,000-address B2B benchmark found.

The most useful test is your own. Run a sample of your list, then compare the share each service declined to judge alongside its verdicts. With ZapBounce, 100 free credits a month cover that sample, and the benchmark method shows how we score results against known send outcomes.

Say you give a verifier 10,000 addresses. It returns a clear verdict on 7,000 and declines to judge the other 3,000. Later you learn the truth about every address, and 6,860 of those 7,000 verdicts were right.

On the vendor's scorecard, that's 6,860 out of 7,000, or 98%. It goes on the home page. Score it the way you'd score it as the buyer and the math changes: 6,860 right answers out of the 10,000 addresses you paid attention to, or 68.6%. That sits inside the 31.2% to 70.0% range Hunter measured when it tested 15 verifiers on 3,000 real business addresses in November 2025.

Nothing about the engine changed between those two scores. Only the bottom of the fraction moved. Whenever you see a single accuracy figure, picture the 3,000 that were left out and ask where they went.

There are two ways for a verdict to be wrong, and you feel them differently. A wrong valid sends mail to a dead mailbox. You get a bounce, you see it in a report, and enough of them will hurt your sender reputation.

A wrong invalid is quieter. Somewhere a real person gets deleted from your list and never hears from you again. No report shows it. Say your list has 50,000 people and one verdict in a hundred is a false invalid. That's 500 real subscribers gone, and if each is worth a few dollars a year to you, the cost repeats every year.

So ask a vendor for both error rates, stated apart. A single accuracy figure can hide a tool that rarely lets a bad address through because it throws out good ones freely. For a store with paying customers on the list, that trade is often the more expensive one.