mail1234.corp.generalmills.com has no CNAME records.
Question and response
Question
dig mail1234.corp.generalmills.com. NS
Answer
The response has no answer records.
Authority
generalmills.com. 900 SOA mgoextdns1.genmills.com. dom\.admin.genmills.com. 15897 900 600 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0