mx.sgnic.sg has no CNAME records.
Question and response
Question
dig mx.sgnic.sg. NS
Answer
The response has no answer records.
Authority
sgnic.sg. 1312 SOA ps.sgnic.sg. postmaster.sgnic.sg. 2349569773 21600 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0