A catch-all domain accepts mail for every address, whether the mailbox exists or not. That single fact is why "catch-all" is the most misunderstood result in email verification — and why honesty about it matters.
When a mail server is set to accept-all, an SMTP probe to anything@the-domain comes back accepted — even for an address nobody ever created. So a real mailbox and a fake one look identical from the outside. Any tool that reports a catch-all address as a confident "valid" is guessing.
Catch-all addresses are common on business domains (Microsoft 365 / Google Workspace with a catch-all rule). Treating them as "valid" inflates your deliverable count and can hurt your sender reputation when the invalid ones bounce later. Treating them all as "bad" throws away real customers. The right move is a separate, lower-confidence segment.
A catch-all (or "accept-all") domain is configured to accept mail for every possible address, even ones that don’t exist. So info@, sales@ and randomstring@ all get accepted at the SMTP level.
Not with certainty. Because the server accepts every address, an SMTP probe can’t distinguish a real mailbox from a non-existent one. Honest verifiers return "catch-all / uncertain" instead of falsely marking it "valid".
To avoid losing mail sent to typo’d or legacy addresses, and sometimes as a spam-trap or forwarding setup. They’re common on business domains using Microsoft 365 or Google Workspace with a catch-all rule.
Treat them as a separate, lower-confidence segment. Don’t assume they’re valid; don’t assume they bounce. Send cautiously (warm IPs, low volume) and watch engagement before trusting them.
Related: Email checker · Email verifier · Insights · Email Infrastructure Index.