Short answer: A catch-all (also called "accept-all") result means the domain's mail server accepts mail to every possible address without revealing whether the specific mailbox exists. We can confirm the domain will receive the message, but the server refuses to confirm the individual mailbox.
Why this happens
Some domains are configured so their mail server says "yes" to every recipient — valid or not — and sorts things out internally afterwards. This is common on:
- Corporate domains with a security gateway in front (Proofpoint, Mimecast, Barracuda, and similar),
- Many Microsoft 365 business tenants,
- Some Google Workspace domains,
- Domains that forward all mail to another inbox.
Because the server accepts everything, there is no way to prove at verification time whether one specific mailbox is real. So instead of a misleading valid, we return catch-all.
Is a catch-all address deliverable?
Often, yes — but it carries more risk than a clean valid. The message will reach the domain; whether it lands in a real mailbox depends on the domain's internal routing, which it does not expose to us.
What we recommend
- Treat
catch-allas "deliverable to the domain, mailbox unconfirmed." - For high-value or transactional sends, catch-all addresses are usually fine.
- For cold outreach at scale, apply extra judgment — catch-all domains can hide non-existent mailboxes.
A catch-all result is charged, because we successfully determined the domain's verification behavior.