---
title: "What Is an MX Record in Email? | Emvero"
description: "Learn how MX records route incoming email, what their preference numbers mean, and how no MX, null MX and broken targets differ."
url: https://emvero.io/glossary/mx-record/
language: en
updated: 2026-10-07
---

All terms

Glossary

# MX record

An MX record names a mail server for a domain and gives its routing preference. It helps a sender choose where to connect, but cannot establish whether an individual mailbox exists.

## Reading an MX record

MX stands for mail exchange. Sending servers look up a receiving domain’s MX records to choose a destination. In the illustrative record `example.com. MX 10 mx1.example.com.`, `mx1.example.com.` names the exchange host and `10` gives its preference.

A domain can publish several exchanges. Lower preference numbers are tried first; equal numbers give hosts equal preference. The selected hostname must resolve to a usable address. [RFC 1035 defines the record fields](https://www.rfc-editor.org/rfc/rfc1035.html#section-3.3.9), and [RFC 5321 describes SMTP routing](https://www.rfc-editor.org/rfc/rfc5321.html#section-5).

## Missing, null and unusable routes

When no MX record exists, SMTP can use the domain’s own A or AAAA address as an implicit route. Emvero may report `IMPLICIT_MX`. An empty MX answer alone cannot establish that the domain receives no mail; the [guide to domains without MX records](https://emvero.io/blog/domain-without-mx-record/) explains this fallback.

A null MX explicitly declares that the domain accepts no mail. It consists of a single MX record whose exchange is `.`, and must not appear alongside ordinary exchanges. Emvero can report `NULL_MX`. [RFC 7505 defines null MX](https://www.rfc-editor.org/rfc/rfc7505.html#section-3).

A published exchange hostname may have no usable address. If no usable destination remains, the route is unresolved and Emvero can report `MX_UNRESOLVABLE`. A temporary DNS failure can also leave the routing question open.

## What a domain check tells you

`MX_FOUND` describes a usable published route; it cannot establish the existence of a named mailbox. `DNS_NXDOMAIN` can identify a nonexistent domain, while `LIKELY_DOMAIN_TYPO` flags a possible spelling mistake. Each finding needs to be read according to its cause.

The free [email domain checker](https://emvero.io/email-domain-checker/) inspects inbound routing without an account. It returns a routing conclusion rather than raw MX hostnames, and cannot establish 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.

`MX_FOUND`

Mail exchangers found

`NULL_MX`

Domain declares that it accepts no mail

`IMPLICIT_MX`

Domain address supplies an implicit mail route

`MX_UNRESOLVABLE`

No usable destination was found for the mail route

`DNS_NXDOMAIN`

Domain does not exist

`LIKELY_DOMAIN_TYPO`

Domain looks like a typo

## Related terms

### SMTP handshake

The greeting and commands used to ask a mail server about a recipient, stopping before message content is sent.

### Catch-all domain

A mail server accepts arbitrary recipients, so acceptance alone cannot establish whether a particular mailbox exists.

### DNS failure

A domain lookup may report nonexistence or a temporary resolution problem. Those outcomes require different handling.

## Compared side by side

### Syntax validation vs SMTP verification

Format rules catch malformed addresses; an SMTP probe can add recipient evidence. Neither guarantees message delivery.

### Domain check vs full verification

Domain depth checks syntax and routing without SMTP. Full verification may add recipient evidence when the destination permits it.

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

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