What is Catch-all domain?
A domain whose mail server accepts email to any address, so verification can't tell you whether a specific mailbox exists.
Some companies configure their mail server to accept everything and sort it out internally. Verification against such a domain always returns "accepted", which is why verifiers report a separate catch-all verdict rather than valid. Catch-all addresses are neither safe nor dead; treat them as higher-risk, send to them in smaller proportions, and let bounces tell you which ones were real.