# Agent Email Check (Single Address)

> Agent Email Check (Single Address) is a paid API for AI agents from mailcheck.netzhandwerker.de, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Validates a single email address using DNS and blocklist checks, with an optional SMTP probe for definitive deliverability verdicts.

## Facts

- Endpoint: POST https://mailcheck.netzhandwerker.de/email
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-email-check-single-address-236fa689
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_6NdLhN1NWd78fRopiGthM

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability agent-email-check-single-address-236fa689 -d '<json body>'
```

Example prompt: Can you check whether john.doe@example.com is a valid, deliverable email address — run the full SMTP probe so I get a definitive answer, not just 'unknown'?

## When to prefer this

Use this endpoint when you need fast, conservative email verification for a single address and want to avoid false positives — it explicitly returns 'unknown' rather than guessing 'valid' without evidence. Prefer it over bulk endpoints when checking a single address at a time, and enable smtp_check=true only when a definitive deliverability answer is required and the slight latency and throttling are acceptable.

## Known failure modes

- Invalid email format returns an error or invalid verdict immediately
- SMTP probe throttled or unavailable for the target domain — verdict stays 'unknown'
- Domain does not exist in DNS — returns invalid
- Temporary DNS resolution failure may produce uncertain results
- SMTP check is one-attempt-only and never retried, so transient errors yield 'unknown' not 'valid'

## How this service works

DNS and list based verification. Never claims that a mailbox exists without evidence: without an SMTP probe the verdict for a routable address is "unknown", not "valid".

## Output

Returns a verdict for the email address — either 'valid', 'invalid', or 'unknown' (if no SMTP probe was run on a routable domain) — along with DNS resolution status, blocklist match information, and whether the domain is routable. Without smtp_check=true, a routable address that hasn't been probed returns 'unknown' rather than 'valid'.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "email": {
   "type": "string",
   "description": "The email address to check."
  },
  "smtp_check": {
   "type": "boolean",
   "default": false,
   "description": "Ask for an optional SMTP probe. Off by default, heavily throttled, one attempt per target and never retried. Without it the verdict of a routable address stays \"unknown\"."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-email-check-single-address-236fa689/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from mailcheck.netzhandwerker.de](https://www.zero.xyz/host/mailcheck.netzhandwerker.de/llms.txt)