ns.kolo.net has no MX records.
Question and response
Question
dig ns.kolo.net. MX
Answer
The response has no answer records.
Authority
kolo.net. 300 SOA ns.kolo.net. hostmaster.kolo.net. 2025120801 5400 900 1209600 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0