mx.vodafone.es has no CNAME records.
Question and response
Question
dig mx.vodafone.es. NS
Answer
The response has no answer records.
Authority
vodafone.es. 10800 SOA ns1.vodafone.es. hostmaster.vodafone.es. 2026022700 43200 7200 1209600 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0