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Catch-All Detector

Detect whether a domain's mail server accepts all email addresses

GET 1 credit /v1/email/catch-all

curl "https://email.toolkitapi.io/v1/email/catch-all?domain=toolkitapi.io" \
  -H "x-api-key: YOUR_API_KEY"

import httpx

resp = httpx.get(
    "https://email.toolkitapi.io/v1/email/catch-all?domain=toolkitapi.io",
)
print(resp.json())

const resp = await fetch("https://email.toolkitapi.io/v1/email/catch-all?domain=toolkitapi.io", {
});
const data = await resp.json();
console.log(data);

# See curl example

Response 200 OK

{
  "domain": "toolkitapi.io",
  "is_catch_all": false,
  "mx_records": ["mx1.toolkitapi.io", "mx2.toolkitapi.io"],
  "method": "smtp_probe"
}

Description

Detect whether a domain's mail server accepts all email addresses

How to Use

1

1. Pass the `domain` as a query parameter (just the domain, not a full email address).

2

2. Check `is_catch_all` — `true` means the server accepts all addresses, `false` means it rejects unknown addresses, `null` means detection was inconclusive.

3

3. If catch-all is detected, treat email validation results for that domain with lower confidence.

4

4. Review `mx_records` to see which mail servers handle the domain.

About This Tool

The Catch-All Detector determines whether a domain's mail server is configured to accept email for any address — even non-existent ones. Catch-all servers accept all messages at the SMTP level, which means individual email validation (RCPT TO probe) cannot reliably distinguish real from fake addresses on that domain.

Knowing whether a domain is catch-all is critical for email list quality. If a domain accepts all addresses, you can't verify individual mailboxes via SMTP, so validation confidence is inherently lower.

Why Use This Tool

Email validation context — Determine if SMTP-level validation is reliable for a domain
Lead quality assessment — Flag catch-all domains where individual address verification isn't possible
List cleaning strategy — Adjust validation thresholds for catch-all vs. non-catch-all domains
Domain intelligence — Understand mail server configuration for a target domain

Frequently Asked Questions

How is catch-all detection performed?

The API probes the domain's MX server with a randomly generated, almost certainly non-existent email address. If the server accepts it (250 response), the domain is catch-all. If it rejects it (550), it's not.

Why would detection be inconclusive?

Some mail servers have greylisting, rate limiting, or delayed rejection that prevents a clear determination. In these cases, `is_catch_all` returns `null`.

Do many domains use catch-all?

Catch-all is common on smaller domains and custom mail servers. Large providers like Gmail and Outlook do not use catch-all — they reject unknown addresses at the SMTP level.

Start using Catch-All Detector now

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