# ProbeKit MTA-STS Check

> ProbeKit MTA-STS Check is a paid API for AI agents from api.probekit.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Validates a domain's MTA-STS policy (RFC 8461) and TLS-RPT record (RFC 8460), including DNS record presence, HTTPS policy file retrieval, certificate validity, mode, max_age, and MX host coverage.

## Facts

- Endpoint: GET https://api.probekit.dev/v1/mail/mta-sts?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/probekit-mta-sts-check-1217a314
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2zbG3oh7ZexRFxtaWh-Xz

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 probekit-mta-sts-check-1217a314
```

Example prompt: Can you check whether mta-sts.example.com has a valid MTA-STS setup — I want to know if the policy file is reachable and correctly signed, what mode it's in, whether all MX hosts are covered, and if there's a TLS-RPT record?

## When to prefer this

Use this endpoint when you specifically need to audit or debug MTA-STS (RFC 8461) and TLS-RPT (RFC 8460) configuration for a domain — it goes deeper than a generic mail check by fetching and validating the HTTPS policy file, checking TLS certificates, verifying MX coverage, and inspecting TLS-RPT. Prefer the full mail report endpoint if you also need SPF, DMARC, and MX together in one call.

## Known failure modes

- Domain does not exist or has no DNS — returns error or empty results
- _mta-sts record missing — flagged as not configured
- Policy file unreachable over HTTPS — connection or certificate error reported
- Policy file redirects detected — flagged as non-compliant per RFC
- MX hosts not covered by policy — listed as uncovered
- TLS-RPT record absent — flagged as missing
- Malformed policy file syntax — parse errors reported
- Invalid or expired TLS certificate on mta-sts hostname — flagged

## How this service works

Check a domain's MTA-STS setup (RFC 8461): the _mta-sts record, the HTTPS policy file with certificate check and no redirects, mode, max_age and whether every MX host is covered, plus the TLS-RPT record (RFC 8460). Use when an agent must tell whether inbound mail is protected against TLS downgrade, or why senders report MTA-STS failures for a domain.

## Output

Returns a structured report covering: presence and content of the _mta-sts TXT DNS record, the HTTPS MTA-STS policy file (fetched without redirects, with TLS certificate validation), policy mode (none/testing/enforce), max_age value, which MX hosts are and aren't covered by the policy, and the TLS-RPT DNS record (RFC 8460) including reporting endpoints.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "title": "DomainInput",
     "required": [
      "domain"
     ],
     "properties": {
      "domain": {
       "type": "string",
       "title": "Domain",
       "examples": [
        "example.com"
       ],
       "maxLength": 1024,
       "minLength": 1
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/probekit-mta-sts-check-1217a314/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.probekit.dev](https://www.zero.xyz/host/api.probekit.dev/llms.txt)