How to Read MX Records and Mail Priorities

An MX (Mail Exchange) record is a DNS record that specifies which mail servers are responsible for receiving email on behalf of a domain.

When an email is sent to an address like user@example.com, the sending server queries DNS for MX records associated with the domain to determine where to deliver the message.

MX records are fundamental to email delivery and are used by platforms such as Microsoft 365 and Google Workspace.

For a deeper DNS-level explanation, Cloudflare provides a useful reference on how MX records work.

• How MX records work

When an email is sent, the sending server follows a structured lookup process:

• Extract the domain from the recipient address such as example.com
• Query DNS for MX records
• Sort results by priority with the lowest value first
• Attempt delivery to the highest priority server
• Fall back to lower priority servers if needed

This process ensures redundancy and reliability in email delivery.

An MX record consists of a priority value and a target hostname.

10 mail.protection.outlook.com

In DNS zone format:

example.com. IN MX 10 mail.protection.outlook.com.

The priority determines delivery order, while the hostname identifies the receiving mail server.

MX priority determines which server is used first. Lower numbers indicate higher priority.

Mail servers will always attempt delivery to the lowest value before trying higher ones.

• 0 is highest priority
• 10 is preferred over 20
• Multiple MX records provide failover
• Equal priorities can enable load balancing

MX records must point to a hostname, not an IP address.

• A records
• AAAA records

That hostname is then resolved using A or AAAA records.

For example, mail.protection.outlook.com resolves to multiple IPs globally, allowing providers to distribute traffic and maintain high availability.

Using hostnames instead of IPs allows providers to scale infrastructure without requiring DNS changes from customers.

Consider the following MX configuration:

0 mx1.examplemail.net
10 mx2.examplemail.net
20 mx3.backupmail.net

Delivery flow:

• mx1.examplemail.net is attempted first
• If unavailable, mx2.examplemail.net is used
• mx3.backupmail.net acts as fallback

This layered approach provides resilience and redundancy.

MX records point to hostnames, which can resolve to multiple IP addresses.

This supports:

• Load balancing across servers
• High availability and failover
• Geographic routing
• Cloud-scale infrastructure

Seeing multiple IPs for a single MX record is expected behaviour.

Microsoft 365:

0 example-com.mail.protection.outlook.com

Google Workspace:

1 aspmx.l.google.com
5 alt1.aspmx.l.google.com
5 alt2.aspmx.l.google.com
10 alt3.aspmx.l.google.com
10 alt4.aspmx.l.google.com

• Official Google MX setup guide

When troubleshooting delivery issues, check:

• MX records exist for the domain
• Priorities are correctly ordered
• MX hostnames resolve to valid IPs
• Records point to the correct provider
• No legacy records remain
• DNS propagation is complete

Misconfigurations are a common cause of email failure:

• Pointing MX to the wrong provider
• Leaving old MX records after migration
• Using IP addresses instead of hostnames
• Incorrect priority values
• Non-resolving hostnames
• Propagation not complete

MX records only define where mail is received. They do not authenticate email.

• SPF
• DKIM
• DMARC

For proper security and deliverability, MX records must be combined with SPF, DKIM, and DMARC.

If email is not being received:

• Query MX records using tools like dig or nslookup
• Check propagation globally
• Confirm MX targets resolve correctly
• Test SMTP connectivity on port 25
• Check firewalls or filtering
• Verify provider configuration
• Review authentication records such as SPF, DKIM, and DMARC

• MX Lookup

You can also validate MX records quickly using DNS Pro.

Follow these practices for reliable delivery:

• Use hostnames, never IP addresses
• Align MX records with your provider
• Use multiple records for redundancy
• Remove unused entries
• Monitor changes during migrations
• Regularly audit DNS and authentication setup

If you want to validate this topic in practice, these DNS Pro tools are the fastest next step.

• MX Lookup
• Email Provider Setup Checker
• Email Security Check