Null MX records: when a domain explicitly accepts no email
A null MX record is an explicit DNS declaration that a domain does not accept mail. It is different from an empty MX lookup or a temporary resolver error. That distinction matters when interpreting verification results or configuring a domain used only for a website.
Open the relevant free tool →Empty MX and null MX are different
Recognize the record
The conventional null MX form uses priority 0 and a single dot as the exchange. The dot is useful; it is not a placeholder to replace with a server hostname. RFC 7505 defines this no-mail signal. A checker should recognize it rather than count the record as an ordinary working exchanger.
Do not confuse it with no answer
An empty MX answer says no MX record was returned. A timeout says the lookup did not finish conclusively. Neither is the same as an explicit no-mail declaration. In a troubleshooting report, preserve which of those outcomes occurred. Otherwise a system may mark a temporary DNS issue as a permanent address failure or treat a no-mail domain as deliverable.
Use it only for a no-mail domain
If you administer a domain that should receive email, a null MX is inconsistent with that goal. Follow your receiving provider’s setup instructions instead. If the domain is intentionally web-only, document that choice so a later administrator does not mistake the record for a broken migration. Take subdomains separately according to their intended use.
Review contradictory configuration
Do not combine a null MX with ordinary exchangers and assume the result is harmless. Check the full DNS record set and resolve conflicting intent. When a provider migration is involved, coordinate the update with mailbox provisioning and testing. Editing DNS alone cannot establish the receiving accounts or confirm that the provider is ready.
Interpret an address check
For an address at a domain that explicitly accepts no mail, a verifier has a clear routing failure to report. That result still says nothing about a person’s identity. If the address came from a customer, ask for a corrected destination. If it came from a CSV, retain the reason in the export so the contact is not reintroduced without review on the next import.
Worked example
example.invalid. IN MX 0 .
Illustrative no-mail record; use your actual domain only when it intentionally accepts no email.