MX Record

What is an MX record

The MX (Mail Exchange) record defines which mail servers will receive email for your domain. When someone sends an email to user@example.com, the sending server makes a DNS query for the MX records of example.com and delivers the message to the listed mail servers.

Structure of an MX record

example.com.  IN  MX  10  mail1.example.com.
example.com.  IN  MX  20  mail2.example.com.
example.com.  IN  MX  30  fallback.example.net.

Fields:

• Priority (10, 20, 30) — lower number = higher priority. The sending server tries the most preferred entries first.
• Hostname — must point to a hostname that has an A/AAAA record. It is not allowed to point to a CNAME or directly to an IP.

How it works

1. The sending server makes a DNS query: «MX records for example.com».
2. It receives the list with priorities.
3. It tries the lowest priority first. If that fails (connection refused, timeout), it tries the next one.
4. Once connected, it performs SMTP delivery.

Multiple MX records with the same priority

If you have two MX records with the same priority, the sending server distributes them randomly/round-robin — useful for load balancing between equivalent mail servers.

Google Workspace example

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

Common mistakes

• MX pointing to an IP or to a CNAME — instead of a proper A/AAAA hostname.
• Missing PTR/Reverse DNS for the mail servers — causes rejections.
• Wrong priorities — avoid random numbers. Use 10, 20, 30 or whatever your provider specifies.
• Missing MX record — some sending servers will fall back to the A record (deprecated behavior), others will reject the mail.

Always pair with SPF, DKIM and DMARC for secure delivery.