What it means
A catch-all (or accept-all) domain is set up to accept mail sent to any address at that domain, whether or not the mailbox exists. That makes standard verification unreliable. The server says yes to every address, so a verifier cannot tell a real person from a typo.
Catch-all results usually come back as risky or unknown. Catch-all setups are common at larger companies, which are often the accounts a B2B team wants most. Dropping every catch-all address loses those accounts, while sending to all of them risks bounces. Catch-all is a server setting, so every address at that company shares the same result.
How we use it
Catch-all domains get a second check of a different kind, since a standard pass on a catch-all tells you little. BounceBan settles catch-alls without sending a message, with DeBounce alongside it.
An address that still cannot be confirmed is dropped or replaced through the Email Verification Waterfall, so the risk never lands on a client's sending domains.