# Null MX

A null MX record is a single MX record with preference 0 pointing at the root, which is how a domain states in DNS that it accepts no mail at all.

Date: 2026-09-10

A null MX record is a single MX record with preference 0 pointing at the root — `0 .` — which is how a domain states in DNS that it accepts no mail at all. It was standardised in RFC 7505 so that a sending server could stop trying immediately rather than queueing and retrying for days.

## What Spaw answers

`mx_found` is false and the reason is [`null_mx`](/docs/reasons/null_mx). The verdict is `undeliverable`, which is the strongest thing the email product says: the domain's own operator has published that nothing can be delivered there.

Undeliverable answers are free, so a list full of null-MX domains costs nothing to clean.

## Why it matters more than an absent record

An absent MX record is ambiguous — it might mean the operator forgot, and RFC 5321 says to fall back to the A record. A null MX is a deliberate statement. Domains used only for a website, or parked, increasingly publish one, which is why it is worth distinguishing from [implicit MX](/glossary/implicit-mx) rather than folding both into "no mail server".

Reference: https://spaw.co/glossary/null-mx