MX records tell the internet where to deliver email for your domain. Understanding them is fundamental to email infrastructure.
Standardized under RFC 1035 and RFC 5321, Mail Exchanger (MX) resource records dictate how remote Mail Transfer Agents (MTAs) locate and connect to the servers responsible for processing incoming mail for your organization.
What are MX Records?
MX (Mail Exchanger) records are DNS entries that specify the mail servers responsible for receiving email for a domain.
An MX record must always point to a fully qualified canonical domain host name (an A or AAAA record), never directly to an IP address or a CNAME alias. For example, Google Workspace publishes records like ASPMX.L.GOOGLE.COM to accept inbound traffic.
How They Work
- Sender queries DNS for recipient domain's MX records: When you send a message, your mail server initiates a DNS lookup for the destination domain. Test live routing with our free MailVeri MX Lookup Tool.
- DNS returns one or more mail servers with priority values: The authoritative nameserver responds with a prioritized list of hostnames.
- Sender connects to lowest priority number first: The sending MTA opens an encrypted TCP socket over port 25 to the server with the highest preference (lowest number).
- Email is delivered to that server: Once accepted, the standard SMTP envelope transaction executes. Learn how protocol probes work in our guide on SMTP verification.
Priority Numbers
Lower numbers = higher priority. Multiple MX records provide failover if primary server is down.
For example, a primary gateway may be assigned priority 10, while backup spooling servers receive priority 20 or 30. If servers share identical numbers, sending MTAs load balance traffic across them automatically.
Conclusion
MX records are the backbone of email delivery. Ensure yours are correctly configured.
Screen your destination lists with MailVeri real-time email verification and ensure your full authentication stack is hardened with our guide to SPF, DKIM, and DMARC explained.