mx.ya.com has no CNAME records.
Question and response
Question
dig mx.ya.com. NS
Answer
The response has no answer records.
Authority
ya.com. 272 SOA dns4.wanadoo.es. hostmaster.orange.es. 490 300 14400 604800 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0