mail4.fiberlink.com has no CNAME records.
Question and response
Question
dig mail4.fiberlink.com. NS
Answer
The response has no answer records.
Authority
fiberlink.com. 222 SOA a1-64.akam.net. maas360-networkadmin.wwpdl.vnet.ibm.com. 2021070251 10800 3600 1209600 500
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0