Catch-all, or accept-all, domains
A catch-all domain accepts every address presented to it, whether it exists or not. SMTP verification becomes powerless there: the server answers favourably in every case. YesWeCheck detects these domains, says so explicitly, returns an unknown status, and charges nothing for that address.
Cette page existe aussi en français : voir la page sur les domaines catch-all en français .
What a catch-all domain is
A catch-all domain, also called accept-all, accepts every address presented to it, including those that match no mailbox. The server answers favourably in both cases, which makes the existence of a mailbox undecidable from the outside. The configuration is deliberate and perfectly legitimate: it avoids losing a message sent to a misspelled mailbox.
The configuration is deliberate and perfectly legitimate. An organisation may want to receive everything that arrives on its domain rather than lose a message addressed to a misspelled mailbox. Sorting happens afterwards, on the inside, under rules the outside world never sees.
Accept-all means exactly the same thing. Both words circulate; the second insists on what the server does, the first on what it does next.
How the detection works
To find out whether a domain accepts everything, the probe presents a second address, drawn at random, on the same session as the requested address. If the server also accepts that address, which does not exist, the domain accepts everything. The randomly drawn local part carries no recognisable marker.
The verdict is shared. A domain recognised as accept-all for one customer is immediately accept-all for every other, in real time as well as in batch processing, without resuming the dialogue with its server.
SMTP verification opens a session with the receiving server, announces the sender and the recipient, then stops before writing the message. No mail arrives in the mailbox being analysed, and the person whose address is verified receives nothing.
| Element | Value | What it changes |
|---|---|---|
| Control address | Drawn at random, with no recognisable marker | The target server cannot spot the probe and skew the verdict |
| Session | The same as the requested address | Both answers come from the same server in the same state |
| Shared verdict | Kept in a fast cache for 24 hours, then permanently | A domain recognised once is recognised for everyone, with no second dialogue |
| Status returned | unknown | No credit charged, and the reason is named in the response |
Measured on 7 September 2026: over 7,800 domains tested, more than 1,600 answer to everything. The figures are rounded down so that they stay true as the table grows.
Where the measurement stops
On a domain that accepts everything, no tool can say whether a mailbox exists: the information is not hidden, it is not emitted. Any answer to the contrary is guesswork, not measurement. The status returned is therefore unknown, and the accept-all reason is written in plain text in the response.
This is the point on which email verification services differ most, and the difference is not technical, it is editorial. Any of them can return valid on a catch-all domain. Doing so trades an honest unknown for a flattering guess, and the guess is settled later, by the bounce.
A credit is charged if and only if SMTP verification was requested and the final status is not "unknown".
What to do with a catch-all address
An unknown status is not a dead end, it is a decision handed back to whoever knows the context. The right move depends entirely on what the address is for, and the four situations below cover most of what an integration actually has to decide.
| Situation | Decision |
|---|---|
| Signing up to a service, in real time | Accept. Refusing an address because its domain accepts everything would mean discarding entire companies whose mail is correctly configured. |
| Acquisition campaign on a cold list | Discard, or handle separately. These addresses inflate the bounce rate unpredictably, and they are not charged, so removing them costs nothing. |
| Cleaning a base of existing customers | Keep. An address already used on an accept-all domain is probably still valid: sending history says more than the probe. |
| Named prospecting on an identified account | Cross check with another source. The domain will not decide, verification has to come from elsewhere, for instance from a human confirmation. |
Read the address validation guide to see the field that carries the catch-all verdict in the response.
Frequently asked questions
- What is a catch-all domain?
- A catch-all domain, also called accept-all, accepts every address presented to it, including those that match no mailbox. The server answers favourably in both cases, which makes the existence of a mailbox undecidable from the outside. The configuration is deliberate and perfectly legitimate: it avoids losing a message sent to a misspelled mailbox.
- Can anyone tell whether an address exists on a catch-all domain?
- On a domain that accepts everything, no tool can say whether a mailbox exists: the information is not hidden, it is not emitted. Any answer to the contrary is guesswork, not measurement. The status returned is therefore unknown, and the accept-all reason is written in plain text in the response.
- Is a catch-all address charged?
- No. The status returned is unknown, and an unknown status is never charged. Detecting that a domain accepts everything is useful to the customer, but it is not an answer about the mailbox that was asked about: charging for it would mean charging for the absence of a conclusion.
- Why do two tools disagree on the same catch-all domain?
- Because some of them return the address as valid instead of returning it as unknown. The server did accept, so a tool can choose to conclude. The result is more flattering and just as wrong: the same address will bounce, and the bounce will have been announced nowhere.
Facts read from the YesWeCheck code base on 7 September 2026.