The check validate that the SOA RNAME is consistent across all authoritative name servers and that the mail domain is valid.
DNSmonitor KB - DNS check KB

SOA RNAME (Mailbox) validation

The check validate that the SOA RNAME is consistent across all authoritative name servers and that the mail domain is valid.

The SOA RNAME (Responsible person name) field specifies the mailbox (email address) of the person or entity responsible for the zone. The email address is derived by replacing the first unescaped dot (.) with an at (@) as shown in the examples below.

The RNAME field support.example.com. is interpreted as the email address support@example.com.

The RNAME field support\.europe.example.com. is interpreted as the email address support.europe@example.com.

The RNAME mailbox is used to get in contact with people responsible for a specific zone in order to for example make them aware of a misbehaving DNS server.

Event severities and messages

WARNING

Mail address to responsible person differs between the name servers. This could indicate inconsistent zone data.

Unless the DNS design dictates otherwise, the SOA RNAME field is inconsistent between the name servers. This can be concerning and is a strong indication that the server in question uses a different source of origin to transfer the zone file from.

The responsible person (SOA RNAME) does not represent a valid email address. Please see section 8 in RFC 1035.

The SOA RNAME field should represent a valid email address (mailbox). RFC 1035 contain information about how a mailbox should be represented in a zone file. Examples can also be found under Solutions, tips & tricks further down in this article.

Name server timed out.

The name server timed out while looking up the MX record for the mail domain in the SOA RNAME. This mean that the mail domain can't be verified and mail to the responsible person might bounce.

UNKNOWN

Unable to perform check due to input data failure.

When this message appear usually one of the queries leading up to the final query have received an empty or garbled query response. Please report this through the normal support channel.

Corrupt or malformed response from nameserver.

The check received a query response with unreadable data fields. Please report this through the normal support channel.

Solutions, tips & tricks

It is advisable to avoid personal mailboxes and use a mailbox for a function instead like support@example.com, dnsmaster@example.com or production@example.com. That way you are less likely to miss any mail concerning the DNS environment.