mut-01.oxalide.net has no MX records.
Question and response
Question
dig mut-01.oxalide.net. MX
Answer
The response has no answer records.
Authority
oxalide.net. 900 SOA ns-1864.awsdns-41.co.uk. admin.oxalide.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0