mailsorter.ash.monster.com has no CNAME records.
Question and response
Question
dig mailsorter.ash.monster.com. NS
Answer
The response has no answer records.
Authority
monster.com. 600 SOA ns1.tmpw.net. hostmaster.tmpw.net. 1771743004 1800 600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0