mailgw1.sectorlink.com has no CNAME records.
Question and response
Question
dig mailgw1.sectorlink.com. NS
Answer
The response has no answer records.
Authority
sectorlink.com. 1800 SOA dolly.ns.cloudflare.com. dns.cloudflare.com. 2397949147 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0