# `implicit_mx`: the domain has no MX record and relies on the address-record fallback

The domain publishes no MX record, so mail would fall back to its own address under RFC 5321; such web-only domains rarely accept mail and are never probed.

- Weight: +30
- Dataset: live-dns
- Read from: `mx_implicit`
- Verdict reasons it comes with: `implicit_mx`

RFC 5321 lets a domain without MX records receive mail at its A or AAAA record. Almost no domain set up that way runs a mail server, so the handshake is skipped and the address is reported as risky rather than tried.

It reads from the mx_implicit field and comes with the implicit_mx verdict reason.

**What to do.** Expect a bounce; at signup, ask for another address.

```json
{
    "email": "mia@brochure-site.example",
    "deliverable": "risky",
    "reason": "implicit_mx",
    "mx_found": true,
    "mx_implicit": true,
    "risk_signals": [
        {
            "signal": "implicit_mx",
            "weight": 30,
            "dataset": "live-dns"
        }
    ]
}
```

Reference: https://spaw.co/docs/signals/implicit_mx