The domain does not resolve
CODE REDWhat it means
example.com returns no DNS answer at all. There is nothing to examine, and no mail, sent or received, can work until it resolves.
How to fix it
Check that the domain is still registered and that its nameservers are correct at the registrar.
Check your own domain
This page describes the condition. To find out whether your domain has it, run the GENERIC test or the full checkup, which examines every record at once.
Understand it properly
This page covers one condition. For the whole picture, How SPF, DKIM and DMARC fit together, or start at the Health Library.
Where this comes from
We judge this against RFC 1035 section 4.1.1. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.
Other GENERIC conditions
DOMAIN_NXDOMAIN
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.