How to Check if a Domain Is Catch-All
A catch-all domain accepts mail for every address, real or not, so a normal SMTP probe cannot tell them apart. Here is how to detect catch-all behavior and what to do about it.
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A catch-all domain is the single hardest case in email verification. The receiving server is configured to accept mail for any local part, so [email protected] and [email protected] both get the same 250 OK. If your verifier only knows how to ask "does this address bounce?", a catch-all domain answers yes to everything and gives you no signal at all.
How to detect it
You cannot detect catch-all by probing the address you care about, because it will pass regardless. The trick is to probe an address you are certain does not exist.
The method:
- Take the domain, say
acme.com. - Generate a random local part that no human would ever own, like
[email protected]. - Run the SMTP probe against that fake address.
If the server rejects the fake address with a 550, the domain is not catch-all: it actually checks whether mailboxes exist, so a 250 for your real address means something. If the server accepts the fake address with a 250, the domain is catch-all, and you have learned that no per-address probe on that domain can be trusted.
The honest verdict for a real address on a catch-all domain is risky, not deliverable. The mailbox might exist, but the server will not confirm it, so claiming deliverable would be guessing.
What to do about a catch-all result
Catch-all is common, especially in B2B, and it is not a red flag by itself. Many legitimate companies run catch-all to forgive typos or centralize triage. How you treat a catch-all address depends on your tolerance:
- Warmed-up sender, low stakes. Keep it. The risk of a bounce is real but modest.
- Cold outreach or a fragile sender reputation. Hold it, or send to it in a small, separate batch you watch closely.
What you should not do is treat a catch-all 250 as proof the mailbox is real. That is exactly the mistake that inflates other tools' accuracy claims.
How to check it
The free catch-all checker runs the fake-address probe for you and tells you whether a domain is catch-all, showing the SMTP reply it got. It does not save the domain you check.
To verify a specific address (and see when it lands on a catch-all domain), use the free email verifier. For the deeper background, read what a catch-all email domain is.
Start with 500 free validation credits. No credit card.
Both Free and Pro run the same scan engine — full SMTP probe, MX lookup, typo, disposable, domain checks, and the evidence chain on every verdict. The difference is the monthly credit pool (Free=500, Pro=100,000) plus Pro's API and MCP access.