---
title: What is an MX Record? Definition and Function | SendHQ
description: Learn how Mail Exchanger (MX) records route incoming email to the correct mail server using DNS priority and hostname mapping.
canonical: https://sendhq.cc/terms/mx-record
last-updated: 2026-08-26
---
# What is an MX Record? Definition and Function

An MX record, or Mail Exchanger record, is a DNS resource record that specifies the mail server responsible for accepting email messages on behalf of a domain. It maps a domain name to a specific mail server hostname, ensuring that SMTP traffic is routed to the correct destination.

## Mechanical Operation

When a sender transmits an email, the sending server performs a DNS lookup for the MX record of the recipient domain. The DNS response provides one or more hostnames and associated priority values. The sending server attempts to deliver the message to the server with the lowest priority number first. If that server is unavailable, it fails over to the next lowest priority server in the list.

## Importance for Senders

While MX records primarily handle inbound mail, they are critical for overall domain health. Many receiving mail servers perform a reverse check to see if a sending domain has a valid MX record. A domain that can send mail but cannot receive it may be flagged as suspicious or a spam source, negatively impacting deliverability.

## Common Operational Mistakes

Common errors include pointing an MX record to an A record or a CNAME instead of a hostname, which violates DNS standards. Another frequent mistake is setting all priority values to the same number, which causes random load balancing rather than intentional failover. Misconfiguring these records leads to bounced emails and lost communications.

## Configuration Example

A typical configuration for a domain using a provider like Google Workspace might look like this: Priority 1: aspmx.l.google.com, Priority 5: alt1.aspmx.l.google.com. The sending server will always try the priority 1 server first. You can use SendHQ or its free tools (https://sendhq.cc/tools) to verify your DNS settings for other authentication records.

## Relationship with SMTP

The MX record acts as the pointer, while the Simple Mail Transfer Protocol (SMTP) is the actual transport mechanism. The MX record tells the internet where the SMTP server is located, and SMTP then handles the handshake and data transfer of the email message across the network.

## Questions teams ask

**Can a domain have multiple MX records?**

Yes, domains often have multiple MX records to provide redundancy. They are ranked by priority numbers to ensure high availability.

**Does an MX record affect outgoing email?**

Directly, no, as it routes incoming mail. Indirectly, yes, because some spam filters check for a valid MX record to verify the sender domain.

**What happens if no MX record is found?**

If no MX record exists, some sending servers may attempt to deliver mail to the A record of the domain, but this often fails in modern environments.

## Primary sources

- [RFC 5321: Simple Mail Transfer Protocol](https://www.rfc-editor.org/rfc/rfc5321) — RFC Editor
- [Cloudflare DNS Documentation](https://developers.cloudflare.com/dns/) — Cloudflare

## Continue learning

[mail protocol smtp](https://sendhq.cc/guides/mail-protocol-smtp.md) [email deliverability](https://sendhq.cc/guides/email-deliverability.md) [email domain verification](https://sendhq.cc/guides/email-domain-verification.md) [smtp relay service](https://sendhq.cc/guides/smtp-relay-service.md)