What is an MX record?
Also called: mail exchange record
An MX record is a DNS entry naming the mail servers that accept email for a domain, each with a priority number where lower is tried first. A domain with no MX record almost never receives mail, which makes the MX lookup the fastest way to remove a large share of bad addresses.
The MX lookup is the step after syntax. The host names also reveal the mail provider: Google Workspace domains point at aspmx.l.google.com or smtp.google.com, Microsoft 365 at *.mail.protection.outlook.com. That tells a verifier how the provider tends to answer mailbox probes.
Strictly, RFC 5321 lets a sender fall back to the domain's A record when no MX exists. In practice a domain with no MX rarely runs a mail server, and a missing MX is often a typo: gmial.com has no mail server, and the useful answer is "did you mean gmail.com?".
A domain can also publish a null MX to state outright that it accepts no mail.
Example
example.com. MX 10 mx1.example.com. and MX 20 mx2.example.com.: mx1 is tried first.How SimpleVerifier handles it
A domain with no usable MX record is returned as invalid · No mail server. When the domain is close to the name of a major free provider, the reason adds a suggestion, for example "did you mean gmail.com?".
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Sources
By SimpleVerifier Team · Last reviewed 2026-10-13 · All 50 glossary terms