ns21.colt.net has no MX records.
Question and response
Question
dig ns21.colt.net. MX
Answer
The response has no answer records.
Authority
colt.net. 3600 SOA ns20.colt.net. eudnsmaster.colt.net. 2024104151 10800 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0