A catch-all email configuration is when a company's mail server accepts messages sent to any address at its domain, even ones that don't correspond to a real mailbox. So `anything@company.com` is "accepted" rather than bounced.
Catch-all domains complicate email verification. Because the server accepts everything, a verification tool can't confirm whether a specific address — say, the one you guessed via pattern-based email guessing — actually belongs to a real person, or just gets swept into a catch-all bucket. The verifier returns "accept-all" rather than a clean valid/invalid.
When you encounter a catch-all domain, the practical move is to lead with extra personalization and a clear subject line, so that even if your message reaches a shared or catch-all inbox, a human is likely to forward it to the right person. Cross-referencing the address against a second source also raises your confidence before you send.