What are MX records and why they matter
MX (Mail Exchange) records are one of the fundamental pillars of email infrastructure on the Internet. Every time you send an email, the sending server needs to know which server should receive the message. This information is obtained by querying the MX records of the recipient domain in DNS. Without properly configured MX records, emails simply cannot be delivered, regardless of how well the rest of the infrastructure is set up.
The mechanism is elegant in its simplicity: when you send an email to user@example.com, your mail server queries DNS for the MX records of example.com. DNS returns one or more records, each with a hostname and a priority value. The sending server attempts delivery starting from the record with the lowest priority number (which indicates the highest preference), falling back to the next ones in case of failure. This system ensures redundancy and reliability in mail delivery.
Anatomy of an MX record
An MX record consists of two main elements: the priority (or preference) and the mail server hostname. The priority is a positive integer — the lower the number, the higher the preference. The hostname must be an FQDN (Fully Qualified Domain Name) that in turn must have a valid A record in DNS. It is important to note that an MX record cannot point directly to an IP address — it must always point to a hostname.
In this example, aspmx.l.google.com with priority 1 is the primary server. If it is unreachable, the sender will try alt1 or alt2 (priority 5, chosen randomly among those with the same priority), and finally alt3 or alt4 (priority 10). This tiered architecture ensures that emails are delivered even if one or more servers go down.
How to diagnose MX record issues
The first step in diagnosing email delivery problems is always to verify the domain's MX records. With our MX Lookup you can instantly query the MX records of any domain and view the priorities, hostnames, and associated IP address resolution. This allows you to quickly identify missing records, unresolved hostnames, or incorrect configurations.
The most common issues include: missing MX records (the domain has no MX records configured), hostnames that do not resolve to a valid IP (the MX record points to a server that does not exist in DNS), identical priorities without load balancing (all records have the same priority causing random distribution), and MX records pointing to CNAMEs (an RFC violation that some servers do not handle correctly).
MX and email authentication: the complete picture
MX records are just one part of the email ecosystem. To ensure delivery and prevent spoofing, it is essential to also configure SPF, DKIM, and DMARC. The SPF record specifies which servers are authorized to send email on behalf of your domain — you can verify it with our SPF Lookup. DKIM adds a cryptographic signature that guarantees message integrity. DMARC unifies SPF and DKIM by defining a policy on how to handle unauthenticated emails.
A complete and secure email configuration requires all these elements working together. MX records handle inbound mail routing, SPF controls who can send, DKIM ensures that the content has not been tampered with, and DMARC defines the consequences for messages that fail authentication checks. Neglecting even one of these elements can compromise your email deliverability.
Best practices for MX configuration
For a robust MX configuration, follow these best practices: always configure at least two MX records with different priorities to ensure redundancy. Make sure all hostnames in MX records resolve correctly to valid IP addresses. Use different priorities (not all the same) to define a clear hierarchy. Verify that mail servers have reverse DNS (PTR) configured, as many receiving servers reject emails from IPs without PTR records.
Regularly check that your servers have not been blacklisted using the Blacklist Check. A blacklisted IP causes silent rejection of emails — a problem that often goes unnoticed until clients or partners report not receiving your messages. Proactive blacklist monitoring is an essential component of enterprise email management.
Finally, always keep MX records up to date after hosting migrations or email provider changes. Stale MX records pointing to decommissioned servers cause all inbound emails to bounce. After every change, use MX Lookup to verify that DNS propagation is complete and that the new records are visible globally.