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Null MX

A Null MX is a special MX record that explicitly says a domain does not accept email. It is useful for a domain that exists for a website or another purpose but has no mail service, because it tells senders not to treat the lack of ordinary MX records as an invitation to try the website's IP address.

What does a Null MX look like?

The record has preference 0 and a destination of . (a single dot), for example example.com MX 0 .. The dot means that there is no mail exchanger. Under the standard, a Null MX must be the domain's only MX record; it cannot be mixed with ordinary mail server destinations.

Without a Null MX, mail systems may fall back to the domain's address records when no MX record exists. That can cause unnecessary delivery attempts and delayed failure notices. A Null MX clearly states that the domain does not handle inbound email. It does not block someone from sending mail that uses the domain as a visible address, and it does not prove that messages claiming to come from the domain are genuine.

Is Null MX the same as a broken MX setup?

No. A Null MX is an intentional declaration that no mail service exists. An absent or misconfigured MX record may instead be an error when the domain is meant to receive mail. The two situations can look similar in a basic DNS listing, so interpret the record in light of the domain's intended use.

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