DNS REFERENCE
What is an MX Record?
The mail routing record of the Domain Name System, directing incoming emails to the correct mail exchange servers.
Understanding the Mail Exchange (MX) Record
An MX Record (short for "Mail Exchange Record") specifies the mail servers responsible for accepting email messages on behalf of a domain name.
When someone sends an email to user@example.com, the sending mail server looks up the MX records for the domain `example.com`. The DNS response guides the sending server to the correct receiving mail server (such as Google Workspace or Microsoft Exchange servers), where the email is then deposited into the user's inbox.
If a domain lacks any configured MX records, sending mail servers will attempt to fall back and look for standard A records pointing to a web server to try and deliver mail directly to that IP address, though this often fails on modern corporate networks.
MX Priority and Failover
One unique characteristic of MX records is the priority value. This allows domain administrators to list multiple mail servers to ensure uninterrupted mail delivery in case their primary server experiences downtime.
| Host/Name | Priority | Record Type | Points To (Value) |
|---|---|---|---|
| example.com | 10 (Primary) | MX | mail-primary.example.com |
| example.com | 20 (Secondary) | MX | mail-backup.example.com |
Sending mail servers read the priority ranks and will always attempt delivery to the server with the lowest priority number first. If the lowest-numbered server is unreachable or times out, the sender attempts to connect to the next server with a higher priority number.
Query an MX Record in Real Time
Lookup the MX records for any domain to see which mail servers handle its incoming emails:
Rules for MX Configuration
- Must point to hostnames, not IP addresses: MX records must point to a fully qualified domain name (FQDN) that resolves via an A or AAAA record. Pointing an MX record directly to an IP address violates DNS standards.
- Avoid pointing to CNAME aliases: DNS RFC standards state that the destination hostname in an MX record should not be an alias mapped by a CNAME record. While many systems tolerate it, doing so can delay email routing or trigger delivery failures in strict environments.
KEY FACTS
Primary Use
Directing incoming emails to correct mail servers
Unique Field
Priority (lower values take precedence)
Output Value
Priority code + hostname (e.g. 10 mail.example.com)
OTHER DNS EXPLANATIONS