Which email verifiers show coverage as well as accuracy? Start with what the market prints. ZeroBounce claims 99.6% accuracy, Clearout 99.73% and Reoon over 99%. Bouncer and Emailable publish no accuracy percentage at all.
Then read the one outside test. Hunter ran 15 verifiers over 3,000 real business addresses and published the results on 3 November 2025: overall accuracy ran from 31.2% to 70.0%. Both sets of figures can be true, because they divide by different things.
The vendor figure answers a narrow question: of the addresses that got a definite verdict, how many were right? Catch-all domains, Yahoo's anti-harvesting replies, Microsoft throttling and greylisting leave some addresses without a verdict. Take those out of the denominator and a 99% figure gets much easier to reach.
That's the first missing number. Coverage is the share of your list that got a definite verdict at all, and it's what tells you how much of the 99% applies to your file.
The second is the false positive rate: the share of addresses called valid that then bounced. It's the error that costs you. A false negative loses you one contact, while a false positive puts a bounce on your sending record and drags down placement for everyone else on the list.
How to measure both on your own list
Take a sample of a few thousand addresses from your real list, including the business domains. Run the same sample through two or three vendors.
Count the rows each one left without a definite verdict: unknown, risky, accept-all, whatever label that vendor uses. Subtract from the total and you have each vendor's coverage on your data.
Then send to the addresses each one called valid and count the bounces. That's the false positive rate, measured on your list rather than on a benchmark somebody else designed.
Do it on your own list rather than a test file. A consumer list of Gmail addresses and a B2B list behind security gateways produce very different numbers from the same vendor.
What ZapBounce puts on the report
The short version
- Ask every vendor for coverage on your own sample, not only an accuracy claim.
- Measure false positives by sending to the addresses called valid, because a send is the only test that sees them.
- Use your own list for the test, since results shift with list composition.
Questions people ask
Which email verifiers show coverage as well as accuracy?
ZapBounce reports both on every file: coverage as the share of the list that got a definite verdict, with catch-all and unknown counts beside it. For any other vendor, run a sample of your own list and count the rows left without a verdict.
What is a good coverage rate for a B2B list?
It depends mostly on how many catch-all domains the list holds. In one 10,000-address B2B benchmark, about 28% of addresses sat on catch-all domains, and no SMTP check can give those a mailbox-level verdict.
Why is a false positive worse than a false negative?
A false negative removes a contact you could have reached. A false positive puts a bounce on your sending record, which affects placement for every other address on the list.
How large should a test sample be?
A few thousand addresses drawn from your real list, weighted the way your list actually is. A sample that leaves out the hard domains measures the easy part of the problem.