What happens if a domain has no MX record?

Senders fall back to the domain's own address record, which is rarely a mail server, so mail to the domain (including replies and bounces) is usually lost. A domain that should never receive mail can say so with a null MX (MX 0 .).

What does the MX priority number mean?

Lower is tried first. Servers with equal priority share the load, and higher numbers are fallbacks used when the preferred ones do not answer.

Do MX records affect sending?

Not directly: they say where mail to the domain is delivered. They matter to senders because replies and bounces go there, and because some receivers check that a sending domain can receive mail at all.

Free tool

MX record lookup

List a domain's mail servers in priority order, resolve each one to its addresses, spot broken MX records and see which mail provider runs them.

Last updated 2026-10-21

Run it with curl

This tool is also a free API: no account, no key, CORS open. OpenAPI description.

curl "https://sendly.now/api/tools/mx-lookup?domain=example.com"

# Markdown instead of JSON:
curl -H "Accept: text/markdown" "https://sendly.now/api/tools/mx-lookup?domain=example.com"

Problems this lookup catches

No MX records, so mail to the domain falls back to its web server or is lost.
An MX that names an IP address instead of a hostname.
A mail server whose name does not resolve, or resolves to a private address.
A null MX (MX 0 .), which declares that the domain receives no mail.

Questions people ask

What happens if a domain has no MX record?: Senders fall back to the domain's own address record, which is rarely a mail server, so mail to the domain (including replies and bounces) is usually lost. A domain that should never receive mail can say so with a null MX (MX 0 .).
What does the MX priority number mean?: Lower is tried first. Servers with equal priority share the load, and higher numbers are fallbacks used when the preferred ones do not answer.
Do MX records affect sending?: Not directly: they say where mail to the domain is delivered. They matter to senders because replies and bounces go there, and because some receivers check that a sending domain can receive mail at all.

Something on this page out of date, or missing the case you are in? Write to support@sendly.now — we answer our own email. The full technical detail lives in the documentation.