A wildcard publishes the same DKIM key at every selector
URGENTWhat it means
Every selector we asked about on example.com returned the same key, including one we invented. Anyone who can sign with that key can pick any selector name they like and it will verify, so rotating a compromised selector does nothing and you cannot retire a key without retiring all of them.
How to fix it
Remove the wildcard TXT record under _domainkey and publish each key at its own named selector. Wildcards under _domainkey exist almost always by accident, usually a *.example.com record meant for something else.
Check your own domain
This page describes the condition. To find out whether your domain has it, run the DKIM test or the full checkup, which examines every record at once.
Understand it properly
This page covers one condition. For the whole picture, What is DKIM, selectors and key strength, or start at the Health Library.
Where this comes from
We judge this against RFC 6376 section 3.6.1. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.
Other DKIM conditions
DKIM_WILDCARD_KEY
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.