Fix missing or broken MX records

What this means

When someone emails an address at the domain, their server looks up its MX records to find where to deliver. We found one of three problems:

No MX

The domain has no MX records at all.

Unresolvable MX

An MX record names a host that has no IP address, often a typo or an old provider's server name.

Null MX

The domain says it accepts no email (priority 0, host "."). That's fine if intended.

Why it matters

Under the email standard (RFC 5321, section 5.1), a sender that finds no MX records falls back to the domain's own A record, which is usually the web server. That server rarely accepts email, so messages are delayed for days and then bounce. An MX pointing at a name with no address fails the same way, and the sender only finds out when the bounce arrives.

How to confirm it

From a terminal, dig example.com MX lists the records. Then look up each host name: dig mail.example.com A should return an address.

How to fix it

Add the MX records your email provider gives you, in the DNS provider that holds the domain's records, and delete any left over from a previous provider.

1  smtp.google.com

Domains that never receive email

For parked domains and ones that only exist for a website, publish a null MX (RFC 7505). Senders then refuse straight away instead of retrying for days. Pair it with records that stop anyone sending as the domain:

MX      0 .
TXT     v=spf1 -all
_dmarc  TXT  v=DMARC1; p=reject

See adding SPF and adding DMARC for more on those two.