Contact address is well-formed
soa.rname-valid
The RNAME is the published route for someone to report a problem with this zone. Nobody checks it until they urgently need it.
A longer write-up of this check has not been published yet. The report itself shows the raw evidence behind every result, which is usually the fastest way to see what was measured.
Run this check on a domain
Contact address is well-formed is one of 49 checks in every report, alongside delegation, mail authentication, TLS and registration.