Wildcard Mx and a Dns Record Conflict
A random problem I’ve just encountered by discovering that my email is broken. You can have a wildcard MX record (*.domain), which will handle all subdomains not defined by other records.
A common mistake is thinking that a wildcard MX for a zone will apply to all hosts in the zone. A wildcard MX will apply only to names in the zone which aren’t listed in the DNS at all. RFC1912
So, in this case, an A record for test.domain will break the email for test@domain. Solution: add a dedicated MX record for this domain (MX test.domain) with the same value as the wildcard. Now, even if the wildcard one is ignored, the client will fall back to the new record.
*.domain MX 10 addr test.domain A 10 adddr2 test.domain MX 10 addr