Authoritative Server - Referrals to root

[Unlisted]

Yes, what I meant to say is that the TLD server for the domain is
handing our NS records out.  Either the domain is on our non-payment
status, been terminated, or removed for aup violations.  Since there is
no SOA anymore there is no NXDOMAIN ttl and therefore we get pounded
with queries asking about that domain.  Whats the best way to cut down
on traffic; serve up SERVFAIL or don't provide referrals to the root
servers on NXDOMAIN?

here is an example:
http://www.dnsstuff.com/tools/dnstime.ch?name=sbiztrade.net&type=A