sendmail3.cos.nhnent.com has no MX records.
Question and response
Question
dig sendmail3.cos.nhnent.com. MX
Answer
The response has no answer records.
Authority
nhnent.com. 180 SOA a1-57.akam.net. webmaster.toastoven.net. 2026022501 21600 1800 1209600 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0