The hostname has the wrong format when creating record with '_'
when you try to create a record with a _ (at least A and CNAME), you have an error message. Exemple we are not able to create "k1._domainkey.dnstest.com. 86400 IN CNAME dkim.mcsv.net." through the ISPConfig web interface, the only way is to do it directly in the bind domain config file