What Is a Mail Exchanger (MX) Record?

A mail exchanger (MX) record is a type of Domain Name System (DNS) record that specifies the mail servers responsible for receiving email on behalf of a domain. Think of it as the postal address for a domain's email: it tells every other server on the internet exactly where to deliver messages sent to that domain. When people ask what "mail exchange" means, this is it, the MX record is the entry in DNS that points incoming mail at the right server.

The DNS works like the internet's address book, translating human-readable domain names such as gmail.com into the IP addresses that computers use to find each other. An MX record sits inside that system and answers one specific question: which server should accept mail for this domain? Without a correctly configured MX record, a domain cannot reliably receive email at all.

How an MX record routes your email

When someone sends a message to an address like [email protected], the sender's mail server does not magically know where gmail.com keeps its inbox. It performs a DNS lookup to find the MX records for the recipient's domain. Those records hand back the hostname of the authorized mail server, and the sending server then opens a connection using the Simple Mail Transfer Protocol (SMTP) and begins the transfer.

The mail exchanger acts as the gateway for everything coming in. It accepts the message on behalf of the domain, checks the sender against its security policies, and passes the email along to the intended mailbox. Take that step away and the message has nowhere to go: it bounces, gets rejected, or quietly disappears.

MX record vs A record

People often confuse the MX record with the A record, because both live in DNS and both involve the domain half of an email address. The difference is what each one points at. An A record maps a domain name to an IP address. An MX record names the server that handles mail for the domain and assigns it a priority.

This is also why "do I need an MX record to send email?" has a nuanced answer. A domain can technically accept mail with only an A record, but most modern email systems and security standards expect properly configured MX records, and domains that lack them often see messages rejected under spam and security policies.

	A record	MX record
What it points to	An IP address	A mail server hostname
Main job	Locate the domain on the network	Route email to the right server
Has a priority value	No	Yes
Required for receiving mail	No (but discouraged)	Yes, in practice

Reading an MX record: server and priority

Each MX record has two main components. The mail server is the fully qualified domain name (FQDN) or IP address of the server assigned to receive mail for the domain, for example gmail-smtp-in.l.google.com. The priority is a numeric value that signals preference, and the rule is counterintuitive: a lower number means higher priority.

When a domain publishes several MX records, sending servers try the lowest-numbered server first. If that server is unavailable, they fall back to the next lowest, and so on. That ordering is what makes failover and load balancing possible. Multiple MX records act as a backup plan, so a single server going offline does not stop mail from arriving, and high volumes can be spread across more than one server.

How to check your MX records

You can inspect any domain's MX records with a standard DNS query tool. On Linux and macOS, use dig; on Windows, use nslookup. The same lookup that troubleshooters run by hand is exactly what a sending server does automatically.

On Linux or macOS:

dig +short gmail.com mx

On Windows:

nslookup -q=mx gmail.com

In both cases the result lists each server with its priority number in front:

5 gmail-smtp-in.l.google.com.
10 alt1.gmail-smtp-in.l.google.com.
20 alt2.gmail-smtp-in.l.google.com.
30 alt3.gmail-smtp-in.l.google.com.
40 alt4.gmail-smtp-in.l.google.com.

Here gmail-smtp-in.l.google.com carries the priority of 5, so servers attempt delivery there first and only fall back to the alternates if it cannot be reached. A web tool like MXToolbox runs the same query from a browser if you would rather not use the command line. If you use a hosted provider such as Google Workspace or Microsoft 365, the provider gives you the exact MX records to publish, and this lookup is the same check email verification runs before it trusts that an address can receive mail.

Why MX records matter for deliverability

MX records do more than route incoming mail, they shape how the rest of the internet judges a domain. When they are configured correctly, email reaches its destination and the domain keeps a healthy sender reputation. When they are wrong or missing, messages bounce, get lost, or never leave the queue, and receiving systems can read that as a sign the domain is not trustworthy.

A handful of issues account for most MX problems: records pointing at the wrong server, duplicate or out-of-order priority numbers, a primary server going down with no backup configured, and authentication gaps where the MX is fine but SPF, DKIM, and DMARC are not. Each of those quietly chips away at delivery rates long before anyone notices a missing message.

Keeping your mail routing solid

An MX record is a small entry in DNS, but it carries a lot of weight: it is the line that tells the world where your email lives. Understanding what it does, how priority works, and how to read a lookup turns a confusing DNS setting into something you can verify in seconds. Get it right and your mail lands where it should; get it wrong and messages vanish without a trace.