Catch-all domain checker

What a catch-all domain is

A catch-all (sometimes accept-all) domain is configured so that its mail server says yes to every recipient, whether or not a mailbox with that name exists. Companies set this up so that misspelt addresses still reach someone, to funnel everything to a shared inbox, or simply because a security gateway sits in front of the real mail system and accepts first, checks later. From the outside the effect is the same: asking the server whether name@domain exists is pointless, because the answer is always 250.

How the probe works

The tool resolves the domain's MX records, connects to the primary exchanger on port 25 and holds an ordinary SMTP conversation: EHLO, MAIL FROM, then RCPT TO for an address with a random 15-character local part that cannot exist. If the server replies 250, the domain accepts everything and is catch-all. If it replies 550, the domain checks names, so deliverable verdicts for real addresses at that domain are trustworthy. A 4xx reply means the server deferred the request (greylisting or a temporary limit), and a connection failure usually means port 25 is filtered or the provider refuses probes; both are reported as undetermined rather than guessed. The transcript is displayed line by line with reply codes, and the session ends with QUIT before any message is sent.

Known provider behaviour is factored in. Yahoo blocks mailbox checks entirely, and consumer Outlook.com accepts every recipient and bounces later, so those are labelled accordingly.

What to do with catch-all addresses

A catch-all address is a bet, not a verdict. Mail often delivers, especially at smaller companies that forward everything to one inbox, but a share will bounce after acceptance. Verifyre scores catch-all addresses as risky and lists the reason so you can apply a policy: send to catch-all contacts who have opened before, warm up new ones in smaller batches, and watch the bounce rate on that segment. In bulk jobs the catch-all status is cached per domain, so a large list from a single company costs one probe, not thousands.