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MX

What is an MX record?

MX records tell other mail servers where to deliver email for a domain. Learn priorities, backup MX, null MX and how to check MX records.

example.com.   3600   IN   MX   10 mx1.example.com.

An MX record (mail exchanger) tells sending mail servers which hosts accept email for a domain. Each record has a preference number and a hostname; lower numbers are tried first.

Priorities

10 mx1.example.com and 20 mx2.example.com mean “use mx1, fall back to mx2”. Records with equal preference share the load.

Requirements

  • The target must be a hostname with A/AAAA records — never an IP address and never a CNAME.
  • If a domain has no MX record, senders fall back to its A/AAAA record. To declare that a domain never receives mail, publish a null MX: 0 . (RFC 7505).

Email deliverability also depends on TXT records for SPF, DKIM and DMARC, and on a matching PTR record for the sending server’s IP address.

Frequently asked questions

Can an MX record point to an IP address?
No. It must point to a hostname, which in turn has A or AAAA records.
What does an MX record of '0 .' mean?
It's a null MX (RFC 7505): the domain explicitly does not accept email, so senders fail fast instead of retrying.

DNS record guides