What is the main purpose of an MX record?

An MX record tells sending mail servers which specific mail servers are authorized and configured to accept incoming emails for your domain name.

What does the priority number mean in an MX record?

The priority number determines the order in which mail servers are contacted. Lower numbers indicate higher priority, meaning senders will try those servers first before moving to higher numbers.

Can an MX record point directly to an IP address?

No, MX records must always point to a fully qualified domain name (hostname) that resolves to an IP address via an A or AAAA record, never directly to an IP.

How long does it take for MX record changes to update?

MX record updates typically take anywhere from a few minutes to 24 hours to propagate globally, depending on the Time to Live (TTL) value set in your DNS configuration.

Why am I not receiving emails even though my MX records look correct?

If your MX records are correct, the issue might stem from missing A records for your mail servers, firewall blocking incoming SMTP traffic on port 25, or SPF and DKIM authentication failures.

What Is an MX Record and How to Check It

An MX (Mail Exchange) record is a type of DNS resource record that specifies the mail server responsible for accepting email messages on behalf of a domain name. Without a properly configured MX record, your domain cannot receive incoming emails from external senders like Gmail or Outlook.

Understanding how these records work and knowing how to inspect them is essential for maintaining reliable business communication and fixing delivery failures.

Understanding the Anatomy of an MX Record

When someone sends an email to user@example.com, their mail transfer agent (MTA) queries the Domain Name System for the MX records of example.com. The returned data tells the sending server exactly where to deliver the message.

An MX record consists of two primary components:

Priority (Preference): A number indicating the order in which mail servers should be contacted. Lower numbers mean higher priority.
Target Hostname: The fully qualified domain name (FQDN) of the mail server handling the traffic.

Why Priority Matters

Priority values allow administrators to set up redundancy and load balancing for email delivery. Typically, an organization configures a primary mail server with a low priority number (such as 10) and one or more backup servers with higher priority numbers (such as 20 or 30).

If the primary mail server goes offline for maintenance or experiences an outage, the sending server automatically attempts to deliver the message to the backup server with the next lowest priority value.

Standard MX Record Syntax

When configuring your domain’s DNS zone file through your registrar or hosting provider, the syntax for an MX record generally looks like this:

example.com.   IN   MX   10   mail.example.com.
example.com.   IN   MX   20   mail-backup.example.com.

In this example, mail.example.com is the preferred destination, while mail-backup.example.com serves as the failover target. Note that the target hostname must resolve to an A or AAAA record; it should never point directly to an IP address.

How to Perform an MX Lookup

Checking your domain's MX records is the first step when troubleshooting email delivery issues, such as messages bouncing or failing to arrive. You can use command-line utilities or web-based interfaces to query public DNS servers.

Using Command-Line Tools

If you prefer using the terminal, both Linux and macOS offer built-in utilities like dig and nslookup.

To check MX records using dig, open your terminal and run:

dig example.com MX

The output will display an "ANSWER SECTION" showing the priority and target mail servers associated with the domain.

To perform the same check using nslookup, run:

nslookup -type=MX example.com

On Windows, nslookup requires you to switch to query type mode first:

nslookup
set type=MX
example.com

Using Web-Based Tools

Command-line tools are powerful, but web utilities offer instant insights without requiring terminal access. You can easily diagnose mail routing configurations by using the MX Lookup tool to query global name servers and verify that your mail servers are reachable.

Common MX Record Misconfigurations

Even experienced administrators occasionally make mistakes when setting up DNS zones. Watch out for these frequent issues:

Pointing to an IP Address: An MX record must always point to a domain name (a hostname), never a raw IPv4 or IPv6 address.
Missing A/AAAA Records: If your MX record points to mail.example.com, but that subdomain lacks a valid A record, sending servers will fail to resolve the destination.
Incorrect Priority Assignment: Setting all mail servers to the same priority can cause erratic load distribution, while using invalid numbers can break RFC compliance.
Conflicting CNAME Records: Never create a CNAME record for a domain apex (like example.com) that also has MX records, as this violates DNS standards.

MX Record Configuration Checklist

Before you finish setting up your email routing, run through this quick checklist to ensure everything is correct:

Verified that the MX record domain matches the intended recipient domain.
Confirmed that priority numbers are set logically (e.g., 10 for primary, 20 for backup).
Ensured the target hostnames point to valid mail servers.
Checked that corresponding A or AAAA records exist for the mail server hostnames.
Performed a live lookup to verify global DNS propagation.