MX record

Reading an MX record

MX stands for mail exchange. Sending servers look up a receiving domain’s MX records to choose a destination. In the illustrative record example.com. MX 10 mx1.example.com., mx1.example.com. names the exchange host and 10 gives its preference.

A domain can publish several exchanges. Lower preference numbers are tried first; equal numbers give hosts equal preference. The selected hostname must resolve to a usable address. RFC 1035 defines the record fields, and RFC 5321 describes SMTP routing.

Missing, null and unusable routes

When no MX record exists, SMTP can use the domain’s own A or AAAA address as an implicit route. Emvero may report IMPLICIT_MX. An empty MX answer alone cannot establish that the domain receives no mail; the guide to domains without MX records explains this fallback.

A null MX explicitly declares that the domain accepts no mail. It consists of a single MX record whose exchange is ., and must not appear alongside ordinary exchanges. Emvero can report NULL_MX. RFC 7505 defines null MX.

A published exchange hostname may have no usable address. If no usable destination remains, the route is unresolved and Emvero can report MX_UNRESOLVABLE. A temporary DNS failure can also leave the routing question open.

What a domain check tells you

MX_FOUND describes a usable published route; it cannot establish the existence of a named mailbox. DNS_NXDOMAIN can identify a nonexistent domain, while LIKELY_DOMAIN_TYPO flags a possible spelling mistake. Each finding needs to be read according to its cause.

The free email domain checker inspects inbound routing without an account. It returns a routing conclusion rather than raw MX hostnames, and cannot establish whether an individual mailbox exists.