mtaproxy3.free.mail.vip.ne1.yahoo.com has no MX records.
Question and response
Question
dig mtaproxy3.free.mail.vip.ne1.yahoo.com. MX
Answer
The response has no answer records.
Authority
ne1.yahoo.com. 600 SOA hidden-master.yahoo.com. hostmaster.yahoo-inc.com. 2026030308 3600 900 604800 600
Additional
. 0 OPT ; payload 1272, xrcode 0, version 0, flags 0