sa2-smtp.onbmc.com has no CNAME records.
Question and response
Question
dig sa2-smtp.onbmc.com. NS
Answer
The response has no answer records.
Authority
onbmc.com. 37875 SOA pdns203.ultradns.com. nikhilk_kulkarni.bmc.com. 2015371878 10800 3600 2592000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0