The domain-specific part of the SML DNS zone (e.g., ‘mydomain’ for
mydomain.sml.dns.zone).
SML domain should be up to 63 characters long, should only contain alphanumeric and hyphen characters,
should not start with a digit nor a hyphen and should not end with a hyphen.
The SML subdomain is already defined!
Domain with empty sml subdomain already exists!