Domain declares that it accepts no mail
NOTEWhat it means
example.com publishes a null MX, which tells the world it never receives mail. Senders fail fast instead of retrying for days. If that is deliberate, it is exactly right.
How to fix it
No action needed, unless this domain is supposed to receive mail, in which case replace the null MX with real mail exchangers.
Check your own domain
This page describes the condition. To find out whether your domain has it, run the MX test or the full checkup, which examines every record at once.
Understand it properly
This page covers one condition. For the whole picture, Why mail lands in spam, in the order worth checking, or start at the Health Library.
Where this comes from
We judge this against RFC 7505 section 3. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.
Other MX conditions
MX_NULL
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.