mail.uu.net has no MX records.
Question and response
Question
dig mail.uu.net. MX
Answer
The response has no answer records.
Authority
uu.net. 3600 SOA AUTH00.NS.UU.NET. hostmaster.UU.NET. 100019035 3600 900 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0