Catch-All Checker

01 what a catch-all domain actually is

A catch-all — or accept-all — domain is a mail server configured to accept mail addressed to anything at the domain. [email protected], [email protected], [email protected]: the server takes them all and sorts it out later. Admins set this up so typos and legacy addresses don't bounce, mail routed through migrations doesn't get lost, and security teams can trap phishing probes in a quarantine box.

It's a perfectly reasonable server configuration. It's also the single biggest blind spot in email verification, because the standard verification technique relies entirely on the server rejecting bad recipients. Catch-all servers never reject anyone — which is exactly the problem.

02 why every verifier says "risky"

Standard SMTP verification works like this: resolve the domain's MX records, open a connection to the mail server, and walk the start of a delivery — EHLO, MAIL FROM, RCPT TO — then hang up before sending anything. The server's reply to RCPT TO is the verdict: 250 means the mailbox exists, 550 means it doesn't.

> RCPT TO:<[email protected]>
< 250 2.1.5 Recipient OK
> RCPT TO:<[email protected]>
< 250 2.1.5 Recipient OK      ← catch-all. the handshake tells you nothing.

On a catch-all domain, the server answers 250 to every recipient — including addresses that were invented a second ago. The handshake carries zero information about whether your specific mailbox is real. An honest tool has to admit that, so it stamps the address risky or accept-all, charges you a credit, and moves on. Catch-all configurations are common across B2B domains, so on a typical prospect list a painful slice of your spend comes back as a shrug.

03 how we resolve the mailbox anyway

The SMTP front door is a dead end on catch-all domains, so we stop asking it. Instead, our proprietary resolution engine takes over — purpose-built algorithms and proprietary data sources that determine which addresses on an accept-all domain actually correspond to a real mailbox:

• Resolution engine: when the handshake is inconclusive, our algorithms work the signals an accept-all server can't hide and decide whether the specific mailbox exists.
• Proprietary data sources: these are combined with our own data to confirm the verdict, independent of how the catch-all is configured.

Because this is independent of the catch-all configuration, a result that any other tool returns as risky collapses into a definitive deliverable or undeliverable. The minority of catch-all domains we can't resolve, we say so honestly — and inconclusive lookups are refunded automatically.

syntax ──→ mx lookup ──→ smtp handshake
                              │
                              ├── 550 ───────────────────→ undeliverable
                              ├── 250, not catch-all ────→ deliverable
                              └── 250, catch-all detected
                                       │
                                       ├── resolution engine ─→ resolved ──→ verdict
                                       └── unresolvable ──────→ risky / unknown (refunded)

04 the rest of the stack

05 pricing

1 lookup = 1 verification. Pay as you go — buy credits, they never expire. Sign up free and get 100 free lookups — no card required. Inconclusive lookups are refunded automatically.

# we resolve catch-all (accept-all) addresses to a real deliverable or undeliverable verdict at 1 credit each — same as any check. most catch-all checkers only flag them. you're only charged when we resolve it; unknown or unresolved results are always free.

create free account → 100 lookups

06 faq