What is a catch-all domain?
Also called: accept-all domain, wildcard mailbox
A catch-all domain is a domain configured to accept mail sent to any address at it, including addresses that do not exist. Because the mail server says yes to everything, a verifier cannot confirm whether a specific mailbox is real, so honest tools return such addresses as risky rather than valid.
Catch-all is a deliberate configuration, common at small companies that want mail to typo'd addresses to still arrive, and at companies using a single shared inbox. From the outside it is indistinguishable from a mail server being generous: every RCPT TO command gets a 250 response whether the mailbox exists or not.
This is the single biggest source of dishonest verification results. A tool that reports catch-all addresses as valid inflates its own accuracy number while handing you addresses that may well bounce. A tool that reports them as invalid throws away addresses that are often perfectly deliverable. Neither is right — the truthful answer is that the mailbox is unconfirmed.
What to do with them depends on your risk tolerance. For cold outreach, send to catch-all addresses in a separate, smaller batch so a wave of bounces cannot damage the reputation of your main sending domain. For a transactional list, treat them as deliverable but monitor bounces closely.
Last reviewed 2026-09-11