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 mistyped addresses to still arrive, and at companies routing everything to one shared inbox. From the outside it looks like a generous mail server: every RCPT TO command gets a 250 response whether the mailbox exists or not.
This is the biggest source of misleading verification results. A tool that reports catch-all addresses as valid looks better on paper while handing you addresses that may bounce. A tool that reports them as invalid throws away addresses that are often deliverable. 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 list of existing customers, treat them as deliverable but watch bounces closely.
Example
[email protected]. A 250 reply to that address means the domain accepts everything, so a 250 for the real address proves nothing.How SimpleVerifier handles it
Before checking the real address, SimpleVerifier asks the server about a randomly generated one. If the server accepts it, the result is risky with the reason Accepts all addresses, never valid.
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By SimpleVerifier Team · Last reviewed 2026-10-13 · All 50 glossary terms