What is MX Record?

MX stands for mail exchanger. Each MX record pairs a preference number with the hostname of a server willing to accept mail for the domain. Sending servers sort the records by preference and try the lowest number first, moving to higher ones if delivery fails — so a domain with two providers might publish 10 mail1.example.net and 20 mail2.example.net.

Rules worth knowing

• The target of an MX record must be a hostname that resolves to an address; pointing it at an IP address or a CNAME is invalid
• Equal preference values are used for load sharing between servers
• A domain with no MX record is treated by many senders as accepting mail at its A or AAAA address, which is rarely what anyone intends
• A single . as the target is the conventional way to declare that a domain accepts no mail at all

Why MX records matter for external exposure

MX records are public and they reveal your mail provider, which is useful to anyone preparing a phishing campaign — the login page to imitate follows directly from the provider name. They also define which hosts must be covered by the rest of your email security configuration: SPF authorises senders, MTA-STS policies list valid MX hostnames, and a stale MX entry pointing at a decommissioned gateway is both a delivery failure and a dangling record.

Common problems

Domains that no longer send or receive mail are frequently left without MX records and without a restrictive SPF and DMARC policy, which makes them attractive to spoof. Parked domains, acquired brands, and redirect-only domains need the same email authentication treatment as production ones.

Related concepts

MX records are the starting point for DNS and email security review, alongside SPF, DKIM, DMARC, and the reverse DNS of the hosts involved.