title: Checking domain name availability with DNS records
body: <p>How accurately can a <strong>domain name's availibility</strong> be determined by checking for the existence of <strong>NS</strong> or <strong>SOA (Start of Authority)</strong> records?</p>
  
  <p>If not, <strong>how</strong> can I determine this as <strong>accurately</strong> as possible <em>without</em> resorting to WHOIS? For example, is it worth checking for MX records if no NS records exist?</p>
  
  <p>I am specifically interested in <strong>.co.za</strong> domains, but the only official, fool-proof way to check availability in the .co.za namespace is to use <a href="http://co.za/whois.shtml" rel="noreferrer">http://co.za/whois.shtml</a>, which limits consecutive checking by IP address.</p>