Understanding MX Records

Learn how MX records direct email delivery and ensure reliable email communication

What is an MX Record?

An MX (Mail Exchange) record tells email servers where to deliver email for your domain. It's like having a map that shows mail carriers which post office handles your mail.

Format:

domain.com.    IN    MX    priority    mail-server.domain.com.

Examples:

# Google Workspace MX records
example.com.    IN    MX    1    aspmx.l.google.com.
example.com.    IN    MX    5    alt1.aspmx.l.google.com.
example.com.    IN    MX    10   alt2.aspmx.l.google.com.

# Microsoft 365 MX records
example.com.    IN    MX    0    example-com.mail.protection.outlook.com.

Simple Explanation

Think of MX records like a postal service for your domain:

MX records are like addresses of post offices that handle your domain's mail
Priority numbers are like instructions telling mail carriers which post office to try first
Lower priority numbers (like 1) are tried before higher numbers (like 10)
Having multiple MX records is like having backup post offices for reliability

Key Components

•
Priority Value
Lower numbers have higher priority. Mail servers try the lowest number first.
•
Mail Server Hostname
The fully qualified domain name of the mail server that handles email.

Common Configurations

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

Microsoft 365

0    domain-com.mail.protection.outlook.com

Common Mistakes

⚠️
Missing Backup Servers
Having only one MX record creates a single point of failure for email delivery.
⚠️
Incorrect Priority Values
Using wrong priority numbers can cause email routing issues and delays.
⚠️
Missing Trailing Dot
Forgetting the trailing dot in mail server hostnames can cause resolution problems.

Best Practices

✓
Use Multiple Servers
Configure multiple MX records with different priorities for redundancy.
✓
Follow Provider Guidelines
Use the exact MX record configuration recommended by your email provider.
✓
Regular Verification
Periodically verify your MX records are correctly configured and resolving.

Security Considerations

🔒
SPF Records
Ensure your SPF record includes all mail servers listed in MX records.
🔒
SSL/TLS Support
Verify your mail servers support encryption for secure email transmission.
🔒
DNSSEC
Consider implementing DNSSEC to protect MX records from tampering.

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