NeverBounce documents its single-check response at developers.neverbounce.com. Every address gets one word in the result field, and each word maps to a plain action on your list. We read that reference on 24 September 2026, and the definitions below quote it where it gives one.
Start with the two clear answers. A valid row means the receiving server accepted the address, so it's safe to mail. An invalid row means the address failed and will hard bounce if you send to it. Delete those before your next campaign, because each one counts against your sender reputation.
Disposable marks a throwaway inbox service. Somebody signed up with an address built to expire, so it rarely reaches a buyer. Most teams drop these rows from a sales list and block them at the signup form.
Catchall is the code people misread most. NeverBounce's docs define it as "a domain wide-setting, also known as Accept-all (Unverifiable)". A catch-all domain answers 250 to every address at the RCPT TO step, real or not, so no SMTP check can confirm the one mailbox. About 28% of addresses in a 10,000-email B2B benchmark sat on catch-all domains, which is why a business list often shows a large catchall share.
Unknown, in the docs' words, means "the server cannot be reached". Greylisting, throttling and timeouts all end there. Wait a day and re-check those rows rather than deleting them, since a greylisting server usually answers on a later try.
ZapBounce uses four results instead of five: valid, invalid, catch_all and unknown. Disposable, role and free-provider are separate true-or-false flags on every row, so you can see that an address is disposable and also on a catch-all domain. The result codes reference lists every reason value. When you re-verify an export, unknown rows and duplicates are never billed, and 1,000 checks cost $5 on the pricing page.
Related questions
What does catchall mean in NeverBounce?
Catchall means the domain accepts mail for every address, so the one mailbox can't be confirmed. NeverBounce's docs call it a domain-wide setting, also known as accept-all. Send to these rows in a small separate batch after your valid rows land cleanly.
Should I delete NeverBounce unknown results?
No, re-check them first. Unknown means the mail server couldn't be reached during the check, often because of greylisting or a timeout. A second pass a day later usually turns part of those rows into valid or invalid.
Is a NeverBounce disposable result the same as invalid?
No. A disposable address can still receive mail for a while, but it sits on a throwaway inbox service built to expire. Most senders drop disposable rows from sales lists anyway, because they rarely reach a real buyer.
How do NeverBounce codes map to ZapBounce results?
Valid, invalid and unknown map one to one, and NeverBounce catchall matches the ZapBounce catch_all result. Disposable becomes a flag in ZapBounce, set beside whichever of the four results the address gets.