mx1.execulink.com has no CNAME records.
Question and response
Question
dig mx1.execulink.com. NS
Answer
The response has no answer records.
Authority
execulink.com. 1870 SOA mallet.execulink.net. sysadmin.execulink.com. 2026010801 158914 300 604800 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0