An MX (Mail Exchange) record is a DNS record that specifies which mail server is responsible for receiving email for a domain. When a message is sent to a domain, the sending mail server checks the domain's MX records to identify where the message should be delivered.
What Does an MX Record Do?
An MX record provides the information needed to route incoming email to the appropriate mail server. A domain can have one MX record or multiple records, depending on how its email receiving system is configured.
MX records are used for receiving email. They do not identify the server used to send outgoing messages. Outgoing email is handled by the sender's mail infrastructure and SMTP.
MX Record Priority
A domain can have multiple MX records, and each record has a priority value. The priority determines the order in which mail servers should be contacted for delivery.
A lower numerical value represents a higher priority. For example:
| Priority | Mail Server |
|---|---|
| 10 | mail1.example.com |
| 20 | mail2.example.com |
The sending mail server attempts delivery to the server with priority 10 first. If that server is unavailable or cannot accept the message, the sending server can attempt delivery to the next available MX server.
Multiple MX records provide alternative mail servers for receiving email and can support continued delivery when a higher-priority server is unavailable.
How Does an MX Record Work?
When an email is sent, the sending mail server first identifies the recipient's domain. It then queries DNS for the domain's MX records.
The MX lookup returns the mail server hostname and its priority. The sending mail server selects the appropriate server, establishes an SMTP connection, and attempts to deliver the message.
An MX record points to a mail server hostname, not directly to an IP address. DNS resolves that hostname to an IP address so the sending mail server can establish the connection.
What Is an MX Lookup?
An MX lookup is a DNS query that retrieves the MX records configured for a domain. The results show which mail servers are responsible for receiving email and the priority assigned to each server.
An MX lookup is useful when checking whether a domain has a mail server configured to receive email or when investigating email delivery problems.