mx.xservers.net has no CNAME records.
Question and response
Question
dig mx.xservers.net. NS
Answer
The response has no answer records.
Authority
xservers.net. 974 SOA nsa.xservers.ro. tehnic.xservers.ro. 2025112608 3600 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0