SimpleVerifier Team · Reviewed
How accurate are email verifiers?
No independent, reproducible accuracy measurement exists, and vendor claims of 97% to 99.7% cannot be checked by a reader. Accuracy depends on your list: a verifier is reliable at providers that say when a mailbox does not exist and cannot confirm anything at catch-all domains, Yahoo or AOL, Microsoft consumer mail or iCloud.
What we measured
We checked one made-up address at each of 51 consumer mailbox providers, twice, on 23 October 2026. 27 of 51 (53%) said plainly that the mailbox does not exist; 10 (20%) accepted every address; 6 (12%) were not probed because they do not confirm mailboxes; 7 (14%) refused our check and 1 deferred it. Both rounds, about 10.5 hours apart, gave the same kind of answer for every provider.
In an audit of 19 verifier sites on 1 and 2 October 2026, eleven quoted an accuracy figure between 97% and 99.73%, none of them checkable, and two gave different figures on different pages. SimpleVerifier does not publish an accuracy percentage, because we have no independent measurement to back one.
Test any verifier yourself
Invent an address at a real company domain and run it. A verifier that does a real SMTP check returns invalid or risky; one that only checks syntax and MX returns valid. Then compare the bounce rate of the valid segment with the result you were promised.
Related questions
- Why do verifiers disagree on the same address?
- They may use different probing methods and IPs, cache results for different periods, and treat catch-all and unconfirmable addresses differently. Some label unconfirmed addresses valid.
Sources
- How mailbox providers answer verification checks, 2026 (SimpleVerifier study, 51 providers, CC BY 4.0)
- Email verifier claims audit (SimpleVerifier, 19 vendors)
Figures marked as ours come from SimpleVerifier’s own dated tests on made-up addresses, published with their data on the research page. No customer data is used, and we publish no accuracy percentage because we have no independent measurement to back one.
Do it now
Test it on a real address first
Type any address. It gets the same check the paid plans run: syntax, the domain’s mail servers and, where the provider allows it, a live mailbox check. Nothing is sent to the address.
Five checks a minute, no account needed. Nothing is sent to the address — we ask its mail server whether the mailbox exists, then disconnect.
Have a list? Sign in with Google and the first 100 addresses are checked free, with results to download. No card.
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