Catch-all email checker

What is a catch-all email address?

A catch-all email address is any address at a domain whose mail server accepts mail for every recipient, whether a mailbox exists or not. Most mail servers reject an address that has no mailbox behind it. A catch-all domain is configured to accept it anyway, so mail to [email protected] is taken in and either routed to a shared inbox, held for review, or quietly discarded. Companies set this up so a misspelled name or a former employee’s address does not bounce a customer’s message.

The setting belongs to the domain, not to an address. If one address at a domain is catch-all, every address at that domain is, which is why this tool asks for a domain rather than a person’s email.

How common is it? It depends on the mail platform and on how each company has configured it, so the only way to know for a given domain is to test it, which is what this tool does. Our guide to catch-all domains explains why companies turn it on and how to treat the results .

How does catch-all email verification work?

It asks the domain’s mail server to accept an address that cannot exist, and reads the reply. We look up the domain’s MX records, then our verification server opens an SMTP connection to the mail host, introduces itself, and names a recipient with RCPT TO. That recipient is a long random string generated on our side for each check — you cannot choose it, so the tool cannot be used to test whether a particular person’s mailbox exists. The connection closes before any message is transmitted.

A 250 response to an address that cannot exist means the server accepts everything: catch-all. A 550 means it checks recipients: not catch-all. Anything else — a temporary 4xx deferral, a timeout, a refused connection, no MX record — is reported as unknown rather than guessed.

Why do email verifiers return accept-all or risky?

Because on a catch-all domain the server’s yes tells you nothing about the address you asked about. An email verifier asks the same question for the address on your list: does this mailbox exist? On an ordinary domain the server answers truthfully. On a catch-all domain it says yes to every address, so the answer for jane@ is the same as the answer for an invented one. A verifier that reports that as valid is passing the server’s indifference off as confirmation.

Honest tools put these addresses in their own bucket instead — risky, accept-all or catch-all depending on the vendor. Some also have an unknown bucket for servers that would not answer at all, which is a different situation: accept-all and unknown results mean different things and deserve different handling.

Can catch-all email addresses be verified?

Not with certainty. Verification without sending relies on the server telling you which mailboxes exist. A catch-all server has decided not to tell anyone, and there is no other channel to ask. Pattern guessing, social profiles and past engagement can raise or lower confidence in a given address, but none of them is the mail server confirming the mailbox.

The same limit applies to this tool’s own answer. It is one probe at one moment. Administrators change their settings, and some servers accept every recipient during the SMTP conversation and only bounce the message after it has been delivered to them — so a domain can look normal here and still produce bounces later. A not catch-all result is strong evidence, not a guarantee.

Do Google Workspace and Microsoft 365 domains use catch-all?

They can, if an administrator turns it on. Google Workspace has a default routing setting that sends misaddressed mail to a catch-all mailbox. Microsoft 365 has no single switch, but admins can get the same effect through how the domain is set up in Exchange Online and a mail flow rule. Neither is the default, so you cannot tell from the provider alone. The probe above shows what the domain actually does.

How should I handle catch-all email addresses?

Send to them separately, in small batches, and never mixed into your confirmed-valid list.

• Segment them. Keep catch-all addresses out of the send that carries your confirmed valid ones, so any bounces land on a list you can measure separately.
• Send in small batches and watch the bounce rate for each batch before sending the next.
• Prefer addresses with independent evidence — a published address, a reply history, or a format the company is known to use.
• Remove hard bounces immediately and do not re-verify them; the bounce is the answer the server would not give earlier.

The full playbook is in how to send to catch-all emails.

How do I check if a domain is catch-all?

1. 1Enter a domain such as acme.example. You can paste an email address instead; only the part after the @ is used.
2. 2Press Check. The tool looks up the domain's MX records and asks the mail server to accept a long random address that cannot exist.
3. 3Read the verdict: catch-all, not catch-all or unknown, with the reason and the domain's MX hosts.
4. 4If it is not catch-all, check individual addresses with the email checker. If it is catch-all, keep those addresses in a separate, smaller send.

Example

You enter

The domain acme.example (an email address works too; only the part after the @ is used).

You get

Catch-all: its mail server accepted a randomly generated address that cannot exist, so single addresses there can't be confirmed. The domain's MX hosts are listed too, lowest first: mx1.acme.example.

Limits

Five checks a minute per IP address, one domain at a time, no account needed.

What do catch-all, not catch-all and unknown mean?

The reply codes are defined in RFC 5321. A temporary 450 4.2.1 is often greylisting, not a verdict.

Who uses this tool, and for what?

Cold emailers

Check the domains on a prospect list before a campaign, then move every address at a catch-all domain into its own slower send so it cannot drag down the main one.

Agencies

Explain to a client why a third of their list came back risky from a verifier: run the biggest domains here and show that their servers accept any address.

Sales ops

Before trusting an email finder's guess at a company, see whether the domain can confirm anything at all. On a catch-all domain the guess stays a guess. The email permutator runs this probe first for the same reason.

What can’t this tool tell you?

• It is one probe at one moment. Administrators change settings, and a domain that rejected the probe today can accept everything next month.
• A server that accepts every recipient during the SMTP conversation and bounces the message afterwards looks catch-all here. The tool cannot tell that apart from a true catch-all.
• Some consumer mailbox providers do not give reliable answers at RCPT TO, so the tool does not probe them and reports unknown.
• Security gateways in front of a company's mail server can answer for it, which may hide how the real server behaves.
• It tests the domain, never a specific person's address, and allows five checks a minute.

Sources

• RFC 5321: Simple Mail Transfer Protocol
• RFC 6647: Email Greylisting
• Google Workspace: Set up default routing

Common questions

How do I check if a domain is catch-all?

Ask the domain's mail server to accept an address that cannot possibly exist. This tool generates a random local part, connects to the domain's MX host, and issues RCPT TO for that address without sending a message. If the server answers 250 accepted, it takes mail for any address and the domain is catch-all. If it answers 550 rejected, it distinguishes real mailboxes from invented ones.

What does accept-all mean in email verification?

Accept-all is another name for catch-all: the domain's mail server accepts every address during the SMTP conversation, whether a mailbox exists or not. Verifiers label these results accept-all, catch-all or risky because the server's yes carries no information about the specific address you asked about.

Can a catch-all email address be verified?

Not with certainty. An SMTP check works by asking the server whether a mailbox exists, and a catch-all server says yes to everything. A verifier can confirm the domain is real and receives mail, but whether jane@ reaches a person or a dead end is only revealed by sending to it and watching for a bounce or a reply.

Why does the checker sometimes say unknown?

Because the probe did not get a clear accept or reject. Common causes are greylisting, where the server defers unknown senders with a temporary error; servers that time out or block verification connections; domains with no MX record; and moments when our probe capacity is in use. Unknown means no conclusion, not a hidden catch-all result.

What does catch-all email mean?

It means the domain's mail server accepts mail for any address at that domain, real or invented, instead of rejecting addresses with no mailbox. The mail usually lands in a shared inbox, waits for review, or is discarded.

Is a catch-all email address valid?

It might be. The domain is real and receives mail, but the server would accept any address, so its yes does not confirm this one. That is why verifiers mark it risky or accept-all rather than valid.

Should I send to addresses at catch-all domains?

Usually yes, carefully. Many catch-all domains belong to real companies, and the address may well be correct. Keep catch-all addresses in their own segment, send to them after your confirmed-valid addresses, use small batches, and remove anything that bounces. Do not mix them into a send that has to stay under a strict bounce threshold.

This tool classifies a domain. To check one address end to end, use the free email checker; for a whole list with catch-all detection on every row, see pricing.