mtaproxy3.free.mail.vip.bf1.yahoo.com has no CNAME records.
Question and response
Question
dig mtaproxy3.free.mail.vip.bf1.yahoo.com. NS
Answer
The response has no answer records.
Authority
bf1.yahoo.com. 600 SOA hidden-master.yahoo.com. hostmaster.yahoo-inc.com. 2026030613 28800 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0