---
title: "Email DNS Errors: NXDOMAIN, SERVFAIL and Timeouts - Emvero"
description: "Understand which DNS answers can reject an email domain, which leave verification unknown, and why no MX record is not the same as no mail route."
url: https://emvero.io/glossary/dns-failure/
language: en
updated: 2026-10-07
---

All terms

Glossary

# DNS failure

A DNS failure prevents verification from obtaining usable domain or mail-routing information. A missing domain and a lookup that could not finish have different consequences for the result.

## When the address domain does not exist

Verification looks up the address domain and its mail route in DNS. The cause of a failed lookup determines how to read `status`, `action` and `reason_codes`.

`DNS_NXDOMAIN` for the address domain establishes that the name does not exist. Emvero can return `undeliverable` with `reject` without contacting a mail server. NXDOMAIN for a target reached through an alias is a routing problem; it does not establish that the original domain is missing. [RFC 2308 defines NXDOMAIN](https://www.rfc-editor.org/rfc/rfc2308.html#section-2.1).

## When the lookup cannot be completed

`DNS_SERVFAIL` records a failed lookup, `DNS_TIMEOUT` records a lookup that exceeded its time limit, and `DNS_DNSSEC_FAILURE` records failed validation of signed DNS data. These conditions leave the domain’s ability to receive mail unresolved. Emvero returns `unknown` with `allow_with_email_confirmation`.

A later lookup may succeed. Sending SMTP clients also defer and retry after temporary DNS errors under [RFC 5321](https://www.rfc-editor.org/rfc/rfc5321.html#section-5.1). A lookup that could not finish does not supply a missing-domain answer.

## When the requested records are absent

`DNS_NODATA` means the name exists but has no records of the requested type, as defined in [RFC 2308](https://www.rfc-editor.org/rfc/rfc2308.html#section-2.2). For example, if `example.com` has no MX record, SMTP may use its A or AAAA address as an implicit route. Emvero checks that possibility. An empty MX answer neither settles delivery nor guarantees that the API returns the NODATA code. The [MX record explanation](https://emvero.io/glossary/mx-record/) covers this fallback.

A contradictory route can produce `DOMAIN_MAIL_ROUTE_MISCONFIGURED`. That route, and a route with no usable destination, remain unresolved. An explicit null MX declares that the domain accepts no mail. The [guide to domains without MX records](https://emvero.io/blog/domain-without-mx-record/) explains these cases.

Read `checks.mail_routing` alongside the status and reasons. The [email domain checker](https://emvero.io/email-domain-checker/) inspects domain evidence, without establishing whether an individual mailbox exists.

## Related reason codes

The API uses these identifiers to explain a check. The notes identify values that the current verification policy or probe does not return.

`DNS_TIMEOUT`

DNS did not answer in time

`DNS_SERVFAIL`

DNS returned a failure

`DNS_NODATA`

No records of the requested type were returned

`DOMAIN_MAIL_ROUTE_MISCONFIGURED`

Contradictory mail routing

`DNS_DNSSEC_FAILURE`

DNSSEC did not validate

## Related terms

### MX record

A DNS record that identifies a domain’s mail servers and their priority. A mail route does not prove that a mailbox exists.

### Greylisting

A temporary SMTP refusal asks the sender to try again. A later attempt may provide more evidence.

[All terms](https://emvero.io/glossary/)

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