What Are MX Records and How to Check Them

What Is an MX Record?

An MX record — short for Mail Exchange record — is a type of DNS record that tells the internet which mail servers are responsible for accepting incoming email on behalf of your domain. Without a valid MX record, no external server knows where to deliver messages addressed to you@yourdomain.com, and email sent to your domain will simply bounce.

MX records live in your domain's DNS zone alongside other record types like A records, CNAME records, and TXT records. Each MX record has two key components:

• Priority (preference value): A number that determines which mail server to try first. Lower numbers mean higher priority.
• Mail server hostname: The fully qualified domain name (FQDN) of the server that should receive mail, for example mail.yourdomain.com or aspmx.l.google.com.

When someone sends you an email, their sending server performs a DNS lookup for your domain's MX records, then attempts to connect to the highest-priority mail server it finds. If that server is unavailable, it falls back to the next-highest priority server — which is why having more than one MX record is considered best practice for redundancy.

How MX Records Affect Email Delivery

MX records sit at the very start of the email delivery chain. If they are misconfigured, missing, or pointing to a hostname that does not resolve, every inbound message to your domain will fail — no exceptions. This can mean:

• Senders receive an immediate bounce with a 5xx permanent failure code
• Senders receive a 4xx temporary deferral and their server keeps retrying for days before giving up
• Email silently disappears if a hosting provider misconfigures a catch-all

Beyond plain delivery, MX records also interact with your SPF record. Your SPF record authorizes specific IP addresses to send mail from your domain, and some configurations reference the MX mechanism (mx) to automatically include the servers listed in your MX records as authorized senders. If your MX records are wrong, that mechanism may authorize the wrong hosts — or fail to authorize the correct ones.

How to Check Your MX Records

The fastest way to inspect your MX records is with the DMARCFlow MX Checker. Enter your domain and the tool performs a live DNS lookup, displays every MX record with its priority value, and flags common problems instantly — no command-line tools or DNS expertise required.

If you prefer the command line, you can use dig on Linux and macOS:

dig MX yourdomain.com

On Windows, the equivalent is:

nslookup -type=MX yourdomain.com

The output will list each MX record as a line containing the priority number followed by the mail server hostname. Checking this regularly — especially after changing DNS providers or migrating email platforms — is a simple but critical step in maintaining reliable email delivery.

What Good MX Records Look Like

A well-configured domain typically has two or more MX records for redundancy. Here is an example of a healthy MX configuration for a domain using a primary and a backup mail server:

In this setup, sending servers always try the priority 10 server first. Only if that server is unreachable do they fall back to the priority 20 backup. Both hostnames must have their own valid A records (or AAAA records for IPv6) that resolve to the correct IP addresses.

For domains hosted on Google Workspace, you will see five MX records with priorities 1, 5, 5, 10, and 10, all pointing to Google's aspmx.l.google.com and similar hostnames. Microsoft 365 uses a single MX record pointing to yourdomain-com.mail.protection.outlook.com. Both are perfectly valid configurations defined by the provider.

Common MX Record Problems

Even small mistakes in MX records can completely disrupt inbound email. These are the most frequent issues encountered in practice:

• Missing MX records entirely: No MX records exist in DNS. Some servers fall back to the domain's A record, but most will bounce the message. Any domain actively receiving email must have at least one MX record.
• MX record pointing to a CNAME: The DNS specification (RFC 2181) explicitly prohibits MX records from pointing to a CNAME. An MX record must point directly to a hostname with an A or AAAA record. Using a CNAME as the MX target causes unpredictable delivery failures across different mail server implementations.
• Mail server hostname does not resolve: The MX record exists, but the hostname it points to has no A record — or the A record points to a decommissioned IP. The result is a connection failure for every inbound message.
• Incorrect priority values: All MX records assigned the same priority causes sending servers to choose one at random, which may be a server that cannot actually accept mail for your domain.
• TTL set too high: A Time-to-Live value of 86400 seconds (24 hours) means DNS changes propagate slowly. During a mail server migration, a high TTL can cause mail to keep arriving at the old server for a full day after you have updated the records.

Next Steps

Verifying your MX records is just one part of a healthy email infrastructure. Once you confirm your mail routing is correct, the logical next step is checking the full picture of your email deliverability — SPF, DKIM, DMARC, and blacklist status all in one place. The DMARCFlow Email Deliverability Checker runs all of these checks simultaneously so you can spot and fix every configuration gap before it affects your inbox placement.