mx.portsit.com has no CNAME records.
Question and response
Question
dig mx.portsit.com. NS
Answer
The response has no answer records.
Authority
portsit.com. 2835 SOA dns01.dipcon.com. registry.ports.net. 2026021500 1800 900 1814400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0