auth00.ns.uu.net has no MX records.
Question and response
Question
dig auth00.ns.uu.net. MX
Answer
The response has no answer records.
Authority
ns.uu.net. 300 SOA AUTH00.NS.UU.NET. hostmaster.UU.NET. 129 3600 900 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0