NeverBounce's API returns five results: valid, invalid, disposable, catchall and unknown. Its docs describe catchall as "a domain wide-setting, also known as Accept-all (Unverifiable)" and unknown as "the server cannot be reached" (developers.neverbounce.com, read 24 September 2026). So accept-all tells you about the domain, not the person.
Here's the mechanism. A verifier offers your address at RCPT TO, then offers a random address nobody could own at the same domain. When both get a 250, you're dealing with an accept-all server, and the first 250 carried no information. Any verifier that runs an SMTP check meets the same wall on these domains.
Expect plenty of them on a business list. About 28% of a 10,000-address B2B benchmark sat on catch-all domains. Yahoo-hosted domains effectively always classify as catch-all too, because Yahoo answers 250 to every probe. A large accept-all share on a B2B file reflects how mail servers are set up, not a fault in the check.
Keep those contacts, but send to them apart from your confirmed addresses. Put them in a smaller batch on a sending domain you can spare, watch the bounce rate on that batch, and remove any address that hard-bounces. Our answer on whether to remove catch-all emails covers the decision in more depth.
Re-check a NeverBounce export with ZapBounce and addresses on accept-all domains come back as catch_all, on their own line in your report. You pay $5 per 1,000 checks, and an address whose server wouldn't answer comes back unknown at no cost. The ZapBounce vs NeverBounce page sets the two services side by side.
Related questions
Should I send to accept-all emails from NeverBounce?
Send to them in a separate, smaller batch rather than dropping them. Around 28% of a B2B list sits on accept-all domains, and a careful send with bounce tracking is the way to learn which of those mailboxes are live.
What is the difference between accept-all and unknown in NeverBounce?
Accept-all means the server answered and accepts any address. Unknown means the server could not be reached, per NeverBounce's docs. The first is a finding about the domain, while the second is no answer at all and is worth re-checking later.
Why are so many of my emails coming back accept-all?
Business domains often run accept-all mail servers, and Yahoo-hosted domains answer 250 to every probe. On a 10,000-address B2B benchmark, about 28% of addresses sat on catch-all domains.
Can any verifier confirm an accept-all email?
No SMTP check can confirm a single mailbox on an accept-all domain, because the server returns 250 for every address. Some services add inference from other data, which is an estimate rather than a protocol answer.