Catch-all domain

Why an unused recipient can be accepted

A catch-all rule allows a mail server to accept addresses whose name before @ has no mailbox of its own. It may route messages to a shared inbox or decide how to handle them later. The rule describes recipient acceptance; it cannot tell you who will read a message.

Suppose a server accepts alex@example.com and a control address with an arbitrary, unassigned name. The control response suggests that the server accepts nonexistent recipients too. Acceptance of alex@example.com then gives no reliable evidence that this particular mailbox exists.

What Emvero can observe

An SMTP handshake names the recipient with RCPT TO. Message content follows at the DATA stage, defined in RFC 5321. Emvero stops before DATA and sends no email. It therefore cannot observe how the server would handle a message after accepting the recipient.

Established catch-all behaviour appears as accept_all: yes with ACCEPT_ALL_DOMAIN. With otherwise usable domain evidence, the result is risky and the recommendation is allow_with_email_confirmation. A recent domain record can support this completed result without a new SMTP session.

accept_all: unknown means the behaviour has not been established. ACCEPT_ALL_UNKNOWN is a recognised reason code, but the current verification policy does not return it. accept_all: no means the domain does not accept arbitrary recipients. Neither value, on its own, establishes whether the submitted mailbox exists.

How to use the finding

At signup, have your application send confirmation if you need evidence of mailbox access. For a stored list, consider the catch-all finding together with how the address was collected and why you intend to send to it.

The free catch-all lookup reads an existing domain record and opens no SMTP session. To check a full address, follow the catch-all verification guide.